SKS-FILES FORUM
SKS Carbines => Unaltered SKS Rifles => General SKS Discussion => Topic started by: Loose}{Cannon on November 29, 2017, 05:57:46 PM
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In a recent brain-storming thread located here (http://sks-files.com/index.php?topic=3758.0), the age old topic came up regarding the large corresponding numbers found stamped into the barrel lug and receiver on threaded barrel actions (minus Yugos). Most people over the years have said these numbers were applied to keep the barrel and receiver together when separated. I for one have never bought into this notion and have been convinced these numbers are some type of numbering/measuring system vital for mating barrels to receivers at the factory while ensuring perfect rotational indexing during the assembly process. Admin GM and RM actually had the light bulb go off at the same time without collaboration as to how these numbers may have been used.
We think that the two numbers on the barrel and receiver that you tend to see on every Russian, Romanian, Albanian, and threaded Chinese SKS are in fact rough indexing numbers that the builders used when mass producing those particular components. From all the data RM has compiled, the numbers run from 0 to 35 for a total of 36 different numbers. As there are 360° in a circle, it would seem that each number indicates ~10° variance in the start of the the thread for ease of indexing the two parts together w/o a lot of trial and error.
If we are right on this, then for example a receiver with a #10 would mate to a #10 and index the barrel within 10° prior to torquing. If, however you took and replaced the correct barrel with a #19, I would expect the indexing of the two parts to be approximately 90° off give or take ~10°. A #28 barrel would be 180° off and so forth.
(https://image.ibb.co/doJMFG/360.png)
For reference here is a quote from myself in the brain-storming thread.
Its nearly impossible to clock the starting position of male or female threads even on the most modern CNC machines yet alone in the 50s.
What your looking at is rotational degrees that are plotted prior to mating of the components. You would mark the witness mark 90° from 12 o'clock and thread the barrel into a jig. This jig would have 360° marks all the way around it in 10° increments from 0 to 35. When you seat the barrel all the way into the threaded jig your witness mark will land on a number. You stamp that number which literally plots the beginning location of the first thread. You do the same on the receiver using a male jig and stamp the number.
You now have receivers and barrels on standby numbered 0 through 35 representing the rotational degree of the begging thread. You achieve perfect index every time you match the numbers.
It explains the witness marks, the numbers, and the entire process of how they indexed barrels to receivers.
So, how can we prove this theory to be fact?
What we propose is that we take two guns from the same country of origin that said numbers are differing by 18 digits which would represent a 180° difference between the two, take the barrels off the receivers, swap both barrels to the apposite receivers, and if we are correct.... We should have two barrels inverted 180° from where they should be when seated. So in short, FSBs and gas-blocks will be facing downward at the 6 o'clock position and the stock ferrule facing upward at the 12 o'clock position.
To put this plan into action, we a have recruited none other then SKSFiles long time member and gunsmith Ben Murray of Murray's Gunsmithing (https://murraysguns.com/) to perform the test.
Below, I present to you the test subjects. One is a 1958 Chinese /26\ marked as a 13, and a 1959/60 letter H series Chinese /26\ marked as a 31. These two numbers were specifically chosen by me from my collection because 31-13=18 and this 'should' represent a difference of 180°.
(https://image.ibb.co/crDh5G/IMG_20171129_155236_DRO.jpg)
(https://image.ibb.co/g7cmXw/IMG_20171129_155226_DRO.jpg)
And just to have a little fun with this, I created this thread as a poll so you can vote whether or not you think our theory holds any water. :) Poll closed with 14 yays, and 0 nays.
Remember, we could very well be completely wrong and have to go back to the drawing board, but atleast we here at SKSFiles are giving it a try. wink1
Results will be posted in two days on the evening of Friday 12/01/17
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Ladies and gentlemen, members of SKSFiles..... We have 180° inverted barrels.
dance2 dance3 locomotive1 ---------------- declare1
For your viewing pleasure I first present to you barrel #31 mounted and torqued on receiver #13. Since the RSBs were loose, we simple rotated them to about where they should align with the rest of the barrel components. The important thing to note is the 180° inverted stock ferrule, gas block, front sight block, and of course the witness marks. wink1
(https://image.ibb.co/i3AzLG/IMG_20171201_095644_DRO.jpg)
(https://image.ibb.co/bzZn7w/IMG_20171201_095933_DRO.jpg)
(https://image.ibb.co/fO3VSw/IMG_20171201_095852_DRO.jpg)
(https://image.ibb.co/dGaMZb/IMG_20171201_095704_DRO.jpg)
(https://image.ibb.co/jzGjnw/IMG_20171201_095913_DRO.jpg)
(https://image.ibb.co/n083fG/IMG_20171201_095947_DRO.jpg)
Now for barrel #13 on receiver #31 we didnt torque the barrel to the receiver. We have ZERO doubt it would have also indexed at exactly 180° also, but we did this to roughly show where mating of the two surfaces began prior to torquing the remainder of the way. BUT, as you can see in the first picture, we hand tightened this barrel and the threads on this one were a bit tight and we didnt get it quite all the way seated by hand. Absolutely no doubt this barrel would have indexed exactly 180° inverted like the other. thumb1
(https://image.ibb.co/bF5oEb/IMG_20171201_100258_DRO.jpg)
(https://image.ibb.co/h0vc7w/IMG_20171201_100229_DRO.jpg)
(https://image.ibb.co/gAS1Zb/IMG_20171201_100205_DRO.jpg)
(https://image.ibb.co/iT2eLG/IMG_20171201_100405_DRO.jpg)
It is in my opinion these rotational indexing reference numbers would have allowed them to achieve within 20° to 30° PRIOR to index and that amount would be torqued until the witness marks align. When we reinstalled the proper barrels on their respective receivers this is exactly what was observed. wink1
And dont fret.... the rifles are back to normal without a single adverse affect. clap1
(https://image.ibb.co/h7PgZb/IMG_20171201_141948_DRO.jpg)
(https://image.ibb.co/jO3aub/IMG_20171201_141940_DRO.jpg)
(https://image.ibb.co/bBXqSw/IMG_20171201_141908_DRO.jpg)
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Can you add an extra choice... a hedge of sorts?
"Probably correct"
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Sorry Boris.... no 50 shades of grey here. :))
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Having replaced two crapped out Yugo barrels with chrome lined Chinese barrels, I can say that witness marks are not a homogeneous thing. The mating parts do have to index properly for the extractor cut to line up correctly, and my two projects required removal of material (maybe a couple thousandths of an inch?) before the barrel indexed properly in the receiver.
I think the experiment will yield exactly the results which are predicted. Great idea to have an independent gunsmith to do the work, too.
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This will be interesting! popcorn1
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popcorn1
X2
I like it! And errrrrrr ummmmm glad your sacrificing yer own rofl
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popcorn1
X2
I like it! And errrrrrr ummmmm glad your sacrificing yer own rofl
Its uh..... removable part? Geez..... it gonna ruin or something?
This isnt any different then unthreading a bayo screw...... on banians no less.
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Its uh..... removable part? Geez..... it gonna ruin or something?
Probably not but the sight will be on the bootom and the bayo on top for evermore!!!
(unless you change them back again)
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With care taking place with both of your carbines, you likely won't even be able to tell that they've been apart when all is done. The mating parts should return exactly as original.
But is is a nice gesture that you volunteered a couple of guinea pigs for the experiment.
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Murray has the right stuffs. :P
Besides.... Ill be hovering over his shoulder. chuckles1
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Ain't no sense in hiding my choice..I'm secure with a big.. YUP!! thumb1
And... I figure if uber nerd Professor RM also came up with the same conclusion.. Some surious stuffs is about to happen..
If'en I'm wrong.. whoopie fart1 I'm used to it, I have been married and wrong for 23 years.. just ask the wife. Ok..fine back to the drawing board.
but at least we here at SKSFiles are giving it a try. wink1
Love it....getting the bobblehead bible out and thumping it, preaching this is fact.. nea1 Proof is fact!! not guessing, not assuming, not bible thumping..
no grey area..
Simply... it is or it isn't.... to be determined 12/01/17 :o thumb1
ya done yet..is it the 1st yet... did it work? senil1
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You aint right! rofl
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I'm with GM...tell Murray to " step on it". I'm getting old waiting popcorn1.... geezer1
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(https://image.ibb.co/doJMFG/360.png)
Just as a nerdy FYI, to find the opposite of any of these 36 numbers the old +2/-2 trick works great.
Either +2 to the first number and -2 from the second or the other way as required.
31 = 3 -2 is 1 and 1 +2 is 3 - 13
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The empirical approach clap1 thumb1 Eagerly awaiting the results.
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Voting "Yes". Agree that that was the correct theory. Now, you're taking the step of actually proving, or disproving the common theory. Too bad more samples couldn't be used. But two's a good start. Looking forward to the results.
Were these indexing marks used on Mausers and other mass-produced milled, threaded receiver rifles?
firstchoice
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Is a (31) considered standard, my letter gun is a (31) also.
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Is a (31) considered standard, my letter gun is a (31) also.
0 to 35 is whats marked on any given gun. 35 is the highest observed.
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Less then 24 hrs and we will know one way or the other. :o
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Less then 24 hrs and we will know one way or the other. :o
Damn... down to hours and minutes... it's like birthing a kid.. the overly nervous anxious anticipation. Besplode Come on myth.. I wanna see a big arse Mythbusters, this myth is "CONFIRMED" sign.. Not "Plausible", not "Busted"... and just to piss the world off.. "We was right" thumb1 rofl2
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Vote now if you haven't as of yet.
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While we are waiting...
My /606\ 1.4m with a short lug has an 8 on the barrel, and a lightly struck, and/or damaged 8 on the receiver...I think. It easily might not be stamped on the receiver at all and the nick and bluing rub there might be messing with my eyes. The 8 on the barrel is pretty darn tiny compared to others I have seen.
The witness mark lines up, but do not appear to have been struck at the same time.
Replacement barrel? It sure doesn't look replaced...bayonet handle wear on the muzzle and not so sharp rifling makes me doubt it.
Thoughts?
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When you get done, and when Gunboards forum issues are all resolved (if ever), please post results over there. Should be an eye-opener. Thanks.
... and waiting. C'mon already!!!
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Are we there yet.......? :)
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About an hour
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https://youtu.be/zKvhVssO348
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About an hour
You know something already. Yeah. You know.
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About an hour
You know something already. Yeah. You know.
Welp, I was there wasn't I? rofl
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This isn't going to be fake news, is it? I can't vote again in the poll.
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This isn't going to be fake news, is it? I can't vote again in the poll.
Murray will verify the results later.....
Voting has been locked. Stand by.... errr, Hurry up and wait. chuckles1
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GO TO PAGE 1 IN THIS THREAD AND SEE THE SECOND POST AFTER THE OP
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Yay yahoo1
This would have been unsolved forever if it hadnt been for you meddling kids!
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No photoshop there. Good work all.
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Next job.
How did the Yugoslavians do it?
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Sticky Time!
Excellent work!!
And Thanks to Murray for the assistance.
Now I'm curious if there is any international compatibility. And for that matter if late Chinese threaded barrels (short and long lugs) and early recievers and vice versa.
I know m08 decribed mating a Chinese barrel to a Yugoslav action, but are thread pitch and spacing the same between all the national variants?
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Next job.
How did the Yugoslavians do it?
The only thing I can think of is they do it like Ben Murray does with the NOS 59/66 barrels on the market. Those barrels come with no flats no extractor cuts, and no gas port. He has to index and torque the barrel, machine the flats while installed, remove the barrel to cut the extractor, then adjust headspace where necessary.
Its worth noting, I bought one of those barrels myself and there are NO inspection stamps which you would think at the state of completion there would be.... so Im not sure if they were even finished.
It could be those barrels were not completed and Yugoslavia could have simply used an ink stick or pencil to mark the barrel and these numbers were later removed during the finishing process.
Also, Considering they only had TWO facilities doing rework on their guns, these numbers may have been redundant for them to stamp.
In addition :P..... They COULD have found the physical numbering of the parts impractical since they were to be placed in a corresponding numbered bin.
One thing the Chinese mastered.... QC the part, dont waste time marking because the entire bin its going into is marked.
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Maybe the Yugoslavs used numbers on twist-tied, hang tags instead of stamps?
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Maybe the Yugoslavs used numbers on twist-tied, hang tags instead of stamps?
Very well possible..... I can think of several ways in which they could have been labeled or organized into bins without the need to physically stamp them. thumb1
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This is just beautiful hypothesis driven, empirical testing, grade A knowledge generation! Stellar work! clap1 thumb1
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dance2
I don't wanna say it, but there is no other way to express my joy... We was right. :) :P
Cross nation compatibility I can see.. how else would they do it with "licensed" copies. Would be interesting to try to verify. If one looks, it wasn't until Russia and China didn't get along, did the SKS change to short lugs, press fit barrels, spike bayonets, their obligation to make it Russias way was gone. Like Yugoslavia, they did it their way, just faster, cheaper, and with less material.
I believe with Yugoslavia's past experience in arms building, Russia handed them a rifle and a spec sheet and said make this. They probably didn't need machines, setups and education to do it like the other nations. They had tons of machenry from WWII, How many years, like 30-40 plus, did they make Mausers and other weapons. They knew how to work with extractor cuts and head space stuff from building massive amounts of Mauser rifles. As long as they stuck to the Warsaw pact caliber 7.62x39, that was what was important, like Czechlosvokia and the Vz52/57 and the Vz58. The Yugoslavian Ak is another example of going against Russia's master Ak design.
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Good Great job SKS junkies. PAX
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Yes, I agree with your logic and think the interpretation in correct.
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I love this place. Awesome work!!!
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So tomorrow I will tell my wife,i can not put up the Christmas lights as I have to pull the stocks off my letter guns and check the alignment numbers !!!!! Thank you,Again.
BARNAUL
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Yugo, North Korean and East German builders must have used a different method.
No angular markings.
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Yugo, North Korean and East German builders must have used a different method.
No angular markings.
Likely tagged or ink marked, or simply numbered by bin. thumb1
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Yugo, North Korean and East German builders must have used a different method.
No angular markings.
Likely tagged or ink marked, or simply numbered by bin. thumb1
Yugoslavia probably put out maybe 15-30k a year total...ust below or just over a 3/4million total, right? And NK and EG couldnt have had too robust of an operation either, I would imagine.
Hang tags, numbered bins, ink or paint.
Seems as if the low production averages would allow for a more simplistic system of index-indentification. Less likelihood of mix ups.
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iirc Yugoslavia only had two rework facilities. This isn't like Russia or China having many small shops across a large territory. The physical stamping of the components was likely not necessary for their system, but that (to me) does not indicate they didn't clock the thread timing on barrels and receivers.
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Neat!
So glad to see something explained with data...and pictures...
A theory transformed to fact, in short order, no less...once collected data, and a couple of guinea pigs were put to the knife wrench.
Just like that...questions become answers....and this locality proves its worth.......aaahhhhgaaaiiiin!
Next SKS-Files mission.... Lightening Cuts
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Whether stamped in the steel or not on a Yugo and others, calibrated male and female threaded jigs would quickly determine the index value if there was any question.
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Great job to all those that went to the trouble, effort, and expense of shaking out the facts here! thumb1 clap1
Not that it happens that often, but someone wanting to replace a barrel on a threaded barrel Chinese SKS now has the advantage of searching for a replacement barrel with an index number matching the host receiver. Like I said, it won't be a large scale of need, but it'd be a big help to use/know if you were changing out barrels. thumb1
Now, I'm curious to know what index numbers that my Chinese threaded barrel rifle use. Guess I'll have a pop-apart party this evening. I may even add a column in my log books for that info. I tend to lean to the OCD side, at times. :)
firstchoice
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Cool thread, and nice work, guys ! thumb1
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Great thread and sorry I missed the vote!
My vote would have been yes.
This indexing method makes perfect sense for ease for of manufacturing for quickly matching receivers and barrels together that will easily time.
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If you really wanted to get anal about how this process was executed. We witnessed the barrels mating angle prior to torquing to be in the neighborhood of 20 to 30 degrees. Not only would they have clocked the timing of the male and female threads to establish the index point, they also would have either advanced the index value of the barrel jig, retarded the index value of the receiver jig, or both in order for the barrels to time somewhere between 20 and 30 degrees EARLY and that remaining amount of rotation to index is all torque. thumb1
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Thought on terminology.
I think it important to point out that, in modern firearm manufacturing the term "barrel indexing" refers to the process of determining the curvature of the bore and then indexing/aligning that curve with the vertical axis of the receiver-- with the curve opening up with the muzzle oriented either at 6 or 12 o'clock.
I think this process is a fairly recent development in the construction of high accuracy long range precision rifles.
But, in the initial "arsenal re-barreling" thread over in the Russian sub-forum, the term "barrel indexing" led me to some confusion in fully understanding the processes that were being described.
I realized finally that the indexing being referred to, likely had nothing to do with the alignment of bore curvature and vertical axis of the receiver.
Is vertical alignment of the barrel curvature possibly an aspect of the numbered pairings? And if not, might a refinement of the terminology be in order to mitigate the potential for confusion?
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Its a loose term Boris, lets not over-complicate it.
https://en.wikipedia.org/wiki/Indexing_(motion)
Indexing in reference to motion is moving (or being moved) into a new position or location quickly and easily but also precisely. After a machine part has been indexed, its location is known to within a few hundredths of a millimeter (thousandths of an inch), or often even to within a few thousandths of a millimeter (ten-thousandths of an inch), despite the fact that no elaborate measuring or layout was needed to establish that location. Indexing is a necessary kind of motion in many areas of mechanical engineering and machining. A part that indexes, or can be indexed, is said to be indexable.
Usually when the word indexing is used, it refers specifically to rotation. That is, indexing is most often the quick and easy but precise rotation of a machine part through a certain known number of degrees. For example, Machinery's Handbook, 25th edition, in its section on milling machine indexing,[1] says, "Positioning a workpiece at a precise angle or interval of rotation for a machining operation is called indexing."[2] In addition to that most classic sense of the word, the swapping of one part for another, or other controlled movements, are also sometimes referred to as indexing, even if rotation is not the focus.
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Not being a machinist, but having watched probably too many videos on rifle accuracy related topics, this is roughly the concept of barrel indexing I was working with...intially:
http://www.mwerksllc.com/barrelindexing.php
Barrel Indexing:
The concept of barrel indexing has been around for a number of years as a method of improving accuracy in rifles....
The majority of barrels, including custom made barrels, have a slight curve in the bore. This curve is generally not considered a defect but normal to the barrel making process. Barrel Indexing is the process of aligning the curve of the barrel to the vertical axis when mounted in the action. In most cases the bore curve will be indexed with the curve down orientation as this position usually provides the best accuracy. The orientation position could vary with a particular barrel. With the barrel indexed in the vertical position the forces acting on the barrel by the bullet during its travel in the horizontal axis are minimized. With the use of a tuner the vertical component of the forces can be more easily modified improving repeatable accuracy performance. Barrel tuners are commonly used on rim-fire bench rest rifles, and may mask the benefits of barrel indexing. An indexed barrel used with a tuning device can improve the competitive features of an already competent rifle. The beneficial affect of an indexed barrel should not be ignored.
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In that example they are indexing the curve of the barrel to the vertical axis when mounted in the action.
In the sks world, were are referring to rotational indexing several premilled locations when torqued to the receiver as observed by witness marks.
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I got to know.. think1 in a mass produced weapon, thats minute of man, designed for basic infantry with minimal training and maintenance and going to be used in harsh conditions, did a curve or barrel bow on the order of .001 make that much difference. Seems like a lot of effort for minimal gain, a target rifle, a sniper riifle yes, there would be a gain, but not a basic going to have the snot beat out of it and shot mercilessly on the battlefield, with a high probability of being lost in a ditch, in a pool of bodies rusting or some other fate.
The accuracy or durability gain would be minimal, if not a nil factor for the time and effort investment put into the task.
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I got to know.. think1 in a mass produced weapon, thats minute of man, designed for basic infantry with minimal training and maintenance and going to be used in harsh conditions, did a curve or barrel bow on the order of .001 make that much difference. Seems like a lot of effort for minimal gain, a target rifle, a sniper riifle yes, there would be a gain, but not a basic going to have the snot beat out of it and shot mercilessly on the battlefield, with a high probability of being lost in a ditch, in a pool of bodies rusting or some other fate.
The accuracy or durability gain would be minimal, if not a nil factor for the time and effort investment put into the task.
That monkey has a valid point right there.
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Thought on terminology.
I think it important to point out that, in modern firearm manufacturing the term "barrel indexing" refers to the process of determining the curvature of the bore and then indexing/aligning that curve with the vertical axis of the receiver-- with the curve opening up with the muzzle oriented either at 6 or 12 o'clock.
I think this process is a fairly recent development in the construction of high accuracy long range precision rifles.
But, in the initial "arsenal re-barreling" thread over in the Russian sub-forum, the term "barrel indexing" led me to some confusion in fully understanding the processes that were being described.
I realized finally that the indexing being referred to, likely had nothing to do with the alignment of bore curvature and vertical axis of the receiver.
Is vertical alignment of the barrel curvature possibly an aspect of the numbered pairings? And if not, might a refinement of the terminology be in order to mitigate the potential for confusion?
A to Q1: No.
A to Q2: No.
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Someone has to sight it in anyway
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Sure hope there's a little popcorn left in y'alls buckets.
Bad things happen when I start thinking so I'm likely to just embarrass myself but a thought occurred to me about this numbering system. No doubt there is a specific purpose, but here's the deal. (actually first of 3 including BBs "bow")
The "thread pitch" (or "space" between each thread) is 1.5mm. That means for every revolution of the barrel, it moves 1.5mm, or .059". So divide that .059" by 36 numbers, and that means they inspected/marked them with difference between each number at just .00163888". Wow, one and a half thousandths of an inch difference?!
Type of material can enter the picture here, but varying amounts of "crush" are accounted for when machining and measuring, in some cases the thread shank length, but more often and more importantly, the headspace and any "indexing" involved. BBs contention "barrel bore bow" might have been involved is highly doubtful, as this would likely only apply to guys at a bench with their ammo being kept at a constant temp in a cooler, until they load and shoot. ::)
At Alpha Arms, we would machine the barrel, allowing that .002" of "crush" would occur with the torquing of the barrel to receiver, meaning chamber was .002" too deep, until barrel was actually screwed on. So far, all these facts fly in the face of inspecting and marking every .0016" difference. If it was only the numbers 0,2,4,6 etc, and .003" and 20 degrees difference between them, then it would seem a little more logical.
And to add, old Springfield 1903's must have been manufactured with at least .005" crush, as they are torqued on the receivers tighter than any other gun we've ever worked on. In some cases, the "take-off" barrel has to be machined in front of the receiver, just to relieve pressure and get them apart.
(3rd deal) Now we know 'Smiths are all crazy... but got an old retired 'Smith buddy that claims he has a video of Chinese SKS manufacturing, with English speaking voice giving descriptions, and while I'll reserve final "say" until it's been viewed, he contends it shows a round barrel being screwed on to the receiver, then both mounted in a mill vise and extractor cut is very next operation. (important fact...this removes the need to install barrel, mark for extractor cut, remove barrel and machine, then re-install the barrel.) That's always been our method as there doesn't appear to be room for normal machining operation that would do this without machining the receiver a little. (sure never seen that)
It's actually a 100 mi drive for me to go see the old AK/FN/HK/AR/Suppressor manufacturer/dealer buddy from the old days, (and he has cats) but I'll try to get a copy of it asap. May even ask him to snail mail it to me as he's the most 'puter illiterate 70 yr old I know.
With "pinned barrel" SKSs, I can see barrels being manufactured complete with all attachments already on it before attaching to the receiver, but threads muddy up the water. If the video shows machining of the extractor cut after barrel is screwed on, it only makes sense they would also then drill gas port hole, machine top and bottom side flats, then install all 4 barrel attachments.
But that leaves us asking...then what are the numbers for!? And likely has good old LC chomping at the bit to come back over and kick my arse! Yes, he was here and very well prepared for the testing, (kudos dude!) and the barrels were swapped and both indexed near bottom dead center, instead of top dead center.
One last thing today...Having removed quite a number of barrels from SKSs, I can say the amount of torque required to remove them varies between guns, even in a group with the same country of origin. And if numbering system was intended to match indexing of threads, the amount of torque used to "set" the barrel, should have been something they paid attention to. So the only thing that would cause us to be fully on board, would be if it was required to drill the gas port hole before chrome lining the barrel, and index numbers were just to get gas port at top center. Then it would all make sense.
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Interesting!
But I have to say, it really all comes down to the video. Most interested in seeing it asap. thumb1
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I could be missing something too, but here it goes. I would assume the recess for the extractor is cut on the face of the chamber before installation of the barrel, so that necessitates that the receiver and barrel be indexed correctly. The 0.0016" per 10 degrees seems like about the right amount of precision to allow for that much crush during torquing in that case.
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If you really wanted to get anal about how this process was executed. We witnessed the barrels mating angle prior to torquing to be in the neighborhood of 20 to 30 degrees. Not only would they have clocked the timing of the male and female threads to establish the index point, they also would have either advanced the index value of the barrel jig, retarded the index value of the receiver jig, or both in order for the barrels to time somewhere between 20 and 30 degrees EARLY and that remaining amount of rotation to index is all torque. thumb1
They literally could have added as much crush/torque as they wished.
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Good stuff Ben. thumb1
I'd be very interested to see what kind of setup allowed the extraction port cut while threaded into the receiver. I can see how the upper radius could be formed by the mill, but that lower radius in such close proximity to the receiver wall I'm just not seeing how to do it quickly and efficiently w/o occasionally kissing the sidewall of the receiver.
(http://image.ibb.co/gpPxxw/23016621_right_chamber.jpg) (http://ibb.co/iPiCVG)
I have a few photo of early Russians that almost seem to have the lower radius under the lip of the receiver wall. Maybe they did it different than the Chinese? Good stuff all around! thumb1
(http://image.ibb.co/gXKxxw/EB538_receiver_chamber.jpg) (http://imgbb.com/)
(http://preview.ibb.co/jVsjcw/E_41_chamber.jpg) (http://ibb.co/gupmqG)
(http://image.ibb.co/c31XVG/249_chamber.jpg) (http://ibb.co/er31Pb)
(http://image.ibb.co/dDEVHw/1171_chamber.jpg) (http://imgbb.com/)
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Now coming from someone who has rebuilt countless engines...
Having removed quite a number of barrels from SKSs, I can say the amount of torque required to remove them varies between guns, even in a group with the same country of origin.
This sounds odd.... sounds as if there is possibly no set torque value. Why the extreme variance....in manufacturing, torque has a spec for a reason.. Sounds like what were they using... the German torque value.....guten-tight and were just lining the marks up.
What I'm saying is.... when I rip out all 26 headbolts from a Cummins ISX, generally there is not to much difference between them when loosening, because they got torqued to a specific value when they were installed....goes like this.....150ftlbs, 300ftlbs and then pull your guts out and twist them another 90degrees. So.....if one is loose......ringy dingy....there an issue, might even be why your pulling the head. Every engine Ive done....Detroit 60, DD15, Mack E7 and E9, Caterpillars, Volvos... all the bolts for the respective engine pull about the same during removal.. unless one is broken, stripped, corroded, etc....
Their torque spec sheet could have read..
if SKS A needs 100ftlbs to line up...Pass
if SKS B needs 200ftlbs to line up...Pass
if SKS C needs 10 ftlbs to line up... FAIL...whoa...hold up start over..
if you rip out threads...you die!
As long as it's guten-tight..... tight....it's good, I bet they knew how far they could go to thread destruction. They just didn't want it loose. Too much torque is as bad, if not worse, than too little. I wonder, was it dry torque, or oiled torque, that can change values as well, a simple drop of oil can alter the final torque.
And either way.. the theory worked.. both were 180 degrees off. :)
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If you really wanted to get anal about how this process was executed. We witnessed the barrels mating angle prior to torquing to be in the neighborhood of 20 to 30 degrees. Not only would they have clocked the timing of the male and female threads to establish the index point, they also would have either advanced the index value of the barrel jig, retarded the index value of the receiver jig, or both in order for the barrels to time somewhere between 20 and 30 degrees EARLY and that remaining amount of rotation to index is all torque. thumb1
They literally could have added as much crush/torque as they wished.
The crush was a side point, just seems like 10 degrees provides about the right amount of crush, as you've pointed out before.
Mainly, I'm a bit skeptical that the extractor recess is cut after the receiver and barrel are joined on the Chinese, Russian and Romanians. If they are cut afterward in some countries, maybe the gunsmith friend saw a video that was mislabeled as Chinese SKS manufacture but was actually Yugoslavian SKS manufacture and that explains why the Serbs didn't use the 0 to 35 numbering method. Do the Yugoslavian or other SKS barrels on the market have an extractor cut?
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If you really wanted to get anal about how this process was executed. We witnessed the barrels mating angle prior to torquing to be in the neighborhood of 20 to 30 degrees. Not only would they have clocked the timing of the male and female threads to establish the index point, they also would have either advanced the index value of the barrel jig, retarded the index value of the receiver jig, or both in order for the barrels to time somewhere between 20 and 30 degrees EARLY and that remaining amount of rotation to index is all torque. thumb1
They literally could have added as much crush/torque as they wished.
The crush was a side point, just seems like 10 degrees provides about the right amount of crush, as you've pointed out before.
Mainly, I'm a bit skeptical that the extractor recess is cut after the receiver and barrel are joined on the Chinese, Russian and Romanians. If they are cut afterward in some countries, maybe the gunsmith friend saw a video that was mislabeled as Chinese SKS manufacture but was actually Yugoslavian SKS manufacture and that explains why the Serbs didn't use the 0 to 35 numbering method. Do the Yugoslavian or other SKS barrels on the market have an extractor cut?
More importantly.... would China actually allow filming of their weapons building program or outside filming in a military weapons facility? Even if it were commercial made SKS, it was possibly still a super secret state run weapons facility in their eyes. Everything is a big ancient Chinese secret.
And yup... Yugoslavia used extractor cuts.
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The nos yugo barrels have no flats, no extractor cut, and zero inspection stamps of any kind. Im not even convinced they are complete units.
When we reinstalled the correct barrels to their respective receivers, I witnessed about 20 degrees of torque to index on one, and about 30 degrees on the second. If you have a worker thread a barrel into the jig and the pre applied timing mark at 3 o'clock (witness mark) lands on 13.5 and they call it a 13 while a dif worker calls it a 14. THEN you apply the same +/- scenario to the receiver using its male jig........
Expect a difference of torque to index from one gun to another. wink1
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The "thread pitch" (or "space" between each thread) is 1.5mm. That means for every revolution of the barrel, it moves 1.5mm, or .059". So divide that .059" by 36 numbers, and that means they inspected/marked them with difference between each number at just .00163888". Wow, one and a half thousandths of an inch difference?!
Bingo.... Pretty amazing what you can do by dividing 1.5mm into a rotational angle of 360/10. Thats the entire purpose of clocking the first thread with a scaled jig. As a few of us have experienced, a few thousands off the receiver face or lug face makes a big difference on where the barrel will ultimately mate and index after torque. It's rather ingenious!
At Alpha Arms, we would machine the barrel, allowing that .002" of "crush" would occur with the torquing of the barrel to receiver, meaning chamber was .002" too deep, until barrel was actually screwed on. So far, all these facts fly in the face of inspecting and marking every .0016" difference. If it was only the numbers 0,2,4,6 etc, and .003" and 20 degrees difference between them, then it would seem a little more logical.
Not sure how much 'crush' would come into play on an sks which is headspaced after the fact via the bottom rear of the bolt. The main objective would be to index the barrel without over/under torquing. As I explained, the jigs reference marks can be laid out advanced or retarded rotationally clockwise or counter clockwise to allow the barrel to mate with the receiver a set degree before index. They could have it 10, 20, 30 etc and the remaining rotation to index the barrel on the witness marks will be a controlled amount of torque.
And to add, old Springfield 1903's must have been manufactured with at least .005" crush, as they are torqued on the receivers tighter than any other gun we've ever worked on. In some cases, the "take-off" barrel has to be machined in front of the receiver, just to relieve pressure and get them apart.
Not sure what the 'crush' on a 1903 bolt action has to do with a communist semiautomatic with a drastically different design and form of headspacing? The 'crush' of the mating material is simply a result of the torque applied when indexing the witness marks, which I believe can be easily controlled, and headspaced after the fact via the bottom rear of the bolt. I guess I'm failing to see how the amount of crush generated when the barrel is torqued to index suggests they 'didnt' use the numbers in the fashion our theory suggests. :-\ In my mind, these numbers ARE a way to control the amount of torque to index and subsequently the amount of crush that comes with it.
(3rd deal) Now we know 'Smiths are all crazy... but got an old retired 'Smith buddy that claims he has a video of Chinese SKS manufacturing, with English speaking voice giving descriptions, and while I'll reserve final "say" until it's been viewed, he contends it shows a round barrel being screwed on to the receiver, then both mounted in a mill vise and extractor cut is very next operation. (important fact...this removes the need to install barrel, mark for extractor cut, remove barrel and machine, then re-install the barrel.) That's always been our method as there doesn't appear to be room for normal machining operation that would do this without machining the receiver a little. (sure never seen that)
We would all love to see this video to see for ourselves. You can hopefully understand the skepticism that comes along with something of this nature with so many variables.
If our theory is correct, they wouldn't be removing the barrel to cut the extractor either..... Its already there when the barrel is installed. thumb1
But that leaves us asking...then what are the numbers for!? And likely has good old LC chomping at the bit to come back over and kick my arse! Yes, he was here and very well prepared for the testing, (kudos dude!) and the barrels were swapped and both indexed near bottom dead center, instead of top dead center.
Laff Ben.... I may come back over there, but it would be to bring another set of rifles. These having 9 numbers apart that would index 90 degrees from 12 o'clock. In fact, the last test one barrel was 180 past index and the other was 180 pre-index, so a new test having 90 degree difference should land one at 3 o'clock and the other at 9 o'clock. Now thats a test to be able to call out two separate orientations on one swap!
We swapped two and torqued one and it wasn't near bottom dead center, it WAS bottom dead center. The other would have been also had we fully seated and torqued it. thumb1
One last thing today...Having removed quite a number of barrels from SKSs, I can say the amount of torque required to remove them varies between guns, even in a group with the same country of origin. And if numbering system was intended to match indexing of threads, the amount of torque used to "set" the barrel, should have been something they paid attention to.
Lots of variables come to mind... Ones like corrosion, but I would completely expect deviations within a certain torque parameter using our theory method, so I do not see the relevance.
So the only thing that would cause us to be fully on board, would be if it was required to drill the gas port hole before chrome lining the barrel, and index numbers were just to get gas port at top center. Then it would all make sense.
I don't think the gas ports are drilled prior to chroming. With our theory, these numbers are not to align the gas port.... They are to rotationally align the lug flats, and the extractor cut and control the torque on index. Ready made barrels and receivers numbered for assembly regardless of the assemblers IQ or location on the planet and basically zero milling required for mating.
The very fact we were able to call out the exact orientation of two barreled actions based spicifically on their index numbers and had them index exactly where predicted is proof of what these numbers are for. But I'm ready to do it again if need be. thumb1
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Ok... maybe I prove something....maybe not.. but :) Extractor cuts after the barrel install nea1 ....well lets look and see if this is possible. I pulled a few SKSs out, my ice cream melted and the X-Files was paused.. cry1
a Chinese /636\... the extractor cut is dead even with the receiver ledge..
(https://dl.dropboxusercontent.com/s/2o6zau00bbeflae/SAM_3030.JPG?dl=0)
A '71 Albanian... the bottom of the extractor cut is just a hair below the receiver ledge think1
(https://dl.dropboxusercontent.com/s/a5xrf3t4obxajxs/SAM_3022.JPG?dl=0)
Huuummmm, well, what say you.. thats some fancy machine work to cut that extractor groove after install... a '50 Russian... the mother of all SKSs
(https://dl.dropboxusercontent.com/s/ciqcbvgcqqtq8ty/SAM_3024.JPG?dl=0)
Not that this one matters.... this is a 416 PS pressed barrel... they was hitting a lick on lining this one up..
(https://dl.dropboxusercontent.com/s/j4zjpwuvu0xm9f4/SAM_3029.JPG?dl=0)
Now everyone is so concerned with Yugoslavia.... how they do it without numbering this or that, popping tags on barrels, binning them...yadda yadda..Guess no one wants to go look and compare them chuckles1 So......... THEY, Yugoslavia did the extractor cut after the barrel install..on M59/66s
Notice the extra cut in the receiver where the extractor cut ends and the receiver ledge begins.. they machined the extractor cut and over into the receiver. if China, Romania or Russia did this....like RM said, they would hit the receiver... and Yugoslavia did thumb1 they in fact machined a little away cutting the extractor groove..
Funny... I've had this bastard for almost 20 years and never noticed... it's an "I" series M59/66
(https://dl.dropboxusercontent.com/s/w295tz6kqbi9nd5/SAM_3027.JPG?dl=0)
(https://dl.dropboxusercontent.com/s/c4lqu194vtcx9hw/SAM_3028.JPG?dl=0)
(https://dl.dropboxusercontent.com/s/fe1rdv1ilpb8ir3/SAM_3032.JPG?dl=0)
For gits and shiggles....this is a "C" series M59.. no receiver/extractor cut like above.. So possibly Yugoslavia modified their process somewhere between the "C" and "I" series
(https://dl.dropboxusercontent.com/s/p4rcgf6de27uaib/SAM_3031.JPG?dl=0)
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Two more I dug up from random places in the house.. chuckles1
[0138] short lug
(https://dl.dropboxusercontent.com/s/ovnkxtg8ts8lphd/SAM_3035a.JPG?dl=0)
Type 84 /106\ short lug
(https://dl.dropboxusercontent.com/s/b21ojenwhg80spv/SAM_3037a.JPG?dl=0)
Seems finding an extractor cut out thats cut below the receiver isn't hard...
Disclaimer..... yes..I realize they are greasy, slimy and nasty..just the way I like'em. I don't shoot them anyway. thumb1
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Not sure what's in this video nobody has seen, but these cuts going below the receiver line highly discredits is validity before even being seen.
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Laff Ben.... I may come back over there, but it would be to bring another set of rifles. These having 9 numbers apart that would index 90 degrees from 12 o'clock. In fact, the last test one barrel was 180 past index and the other was 180 pre-index, so a new test having 90 degree difference should land one at 3 o'clock and the other at 9 o'clock.
I see someones trying to make a few bucks selling to the local 'hood. "See when you turn this gun sideways the sights are right there! I have them for leftys and rightys, how many do you need?" rofl
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Following GMs lead, I took a few pics. wink1
I have discussed these cuts extensively with RM and it is of our opinion that the following list of guns have had their extractor cut PRIOR to being mated to to receiver.
Russian
Chinese
Romanian
Albanian
Yugo LBs and M59s
East German
It is of our opinion that the following list of guns have had their extractor cut AFTER being mated to to receiver.
Yugo 59/66
North Korean
The evidence. Click to enlarge.
(http://preview.ibb.co/dd6sFG/Soviet_Sino.jpg) (http://ibb.co/kDMg9b)
(http://preview.ibb.co/mxi02w/Ghost.jpg) (http://ibb.co/jXqPUb)
(http://preview.ibb.co/gXbbaG/6_Digit.jpg) (http://ibb.co/exGL2w)
(http://preview.ibb.co/h9shFG/2M.jpg) (http://ibb.co/fTYB9b)
(http://preview.ibb.co/c7K7hw/3M.jpg) (http://ibb.co/g6Wypb)
(http://preview.ibb.co/b6k8pb/Letter_V.jpg) (http://ibb.co/inzCFG)
(http://preview.ibb.co/gA0maG/6M.jpg) (http://ibb.co/f0Y6aG)
(http://preview.ibb.co/jXE19b/7M.jpg) (http://ibb.co/goT6aG)
(http://preview.ibb.co/cYU19b/11M.jpg) (http://ibb.co/k11sFG)
(http://preview.ibb.co/kX2Shw/12M.jpg) (http://ibb.co/nxv2FG)
(http://preview.ibb.co/cq8dpb/1_5M.jpg) (http://ibb.co/hiLDNw)
(http://preview.ibb.co/go6sFG/23M.jpg) (http://ibb.co/mp1RaG)
(http://preview.ibb.co/hRfV2w/51_Ruski.jpg) (http://ibb.co/n3SA2w)
(http://preview.ibb.co/cHJiNw/Romy.jpg) (http://ibb.co/eybEUb)
(http://preview.ibb.co/m1gypb/Alby.jpg) (http://ibb.co/nQYYNw)
(http://preview.ibb.co/fnYYNw/EG.jpg) (http://ibb.co/ed7tNw)
(http://preview.ibb.co/jt97hw/NK.jpg) (http://ibb.co/c4C4Ub)
(http://preview.ibb.co/nmWTNw/Long_Barrel.jpg) (http://ibb.co/byOa2w)
(http://preview.ibb.co/fM7w9b/M59.jpg) (http://ibb.co/de5ipb)
(http://preview.ibb.co/c2GOpb/59_66.jpg) (http://ibb.co/kcWChw)
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Great array of pictures clearly showing the differences! I concur, the M59/66 and NK stand out as having extractor groove cuts done post assembly...cuz I knew all of you were just waiting for my expert opinion rofl
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The East German is messing with the rest, right now.
Extractor cut is below receiver ledge.
I have it apart right now, scouring the receiver for any clues as to how they marked it. So far, no good info.
But I'll keep looking.
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The East German is messing with the rest, right now.
Extractor cut is below receiver ledge.
I have it apart right now, scouring the receiver for any clues as to how they marked it. So far, no good info.
But I'll keep looking.
Added your pic.... thanks
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Best I can do for the East German with the extractor cut under the rail ledge:
Since the East Germans had to have some method of clocking, I scoured the receiver for any type of marking. The barrel has very obvious markings.
Barrel stamps: 25275 and 0D70 over 8
While there is a great amount of pitting at the usual left front area, the witness mark can still be viewed. So, if there were any remnants of numbers, they would at least be somewhat visible. But no stamps at all appear on the left front.
The only other markings are found on the right side, and very lightly stamped.
Receiver number, to the best of my ability to read: [K9] and 27.75
Makes no sense to me at all! But I'll release the deciphering hounds with some pics.
(https://i.imgur.com/iSJtv5dl.jpg)
(https://i.imgur.com/ZFjxAzbl.jpg)
(https://i.imgur.com/XLusxqRl.jpg)
(https://i.imgur.com/W8q2UWpl.jpg)
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All fairly indiscernible. ???
But Ill take a shot at it. :P
The 25275 and 0D70, one is a lot/heat number, and the other a part number. Dont ask which is which.
The 8 on the barrel looks to have been applied at a dif time then the ones above and could possibly be an index number.
The receiver number looks like it could actually be 07.75 or 0775 which is pretty darn close to 8! Are the Germans that anal that they would mark a fractional number if the witness mark in the jig plots somewhere between a 7 and 8?
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I was debating whether the receiver number began with a 0 or a 2. Even under the best magnification I can muster with a loupe, it is not a lock for either. So, the 0 could be quite likely.
On the .75 portion. It make sense that it could be a quarterly measured fraction. Maybe someone else with an East German will be so kind as to check their example? Hopefully it will add confirmation to your theory.
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Dont know of any other sksfiles member who has one. Powersurge had one, but sold it. Maybe he has pics of these numbers still? May have to track down some folks on GB M08.
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https://www.ebay.com/itm/304123427928?hash=item46cf2b3c58:g:GmkAAOSwOChhGXuN
Is this a verified zero?
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Yes. They went from 0 to 35. There are no uncommon/rare numbers that I’ve seen. All should/could turn up with equal propensity on old machinery not able to index the threads.