Sleeving SKS bolt head

[theSKSguy45]

Hello me again. I have a project in mind that I’d like to pursue. It’s silly and horribly inefficient but I don’t really care. After the Re-barrel project that I undertook recently I’ve got a feel for more in depth work on these rifles and I’d like to push it further.

That brings me to my question. Can anyone point me in the direction of getting good knowledge on retrofitting a bolt head for a smaller diameter cartridge? I’m basing the idea off of this post https://www.reddit.com/u/Keltecfanboy/s/I3eTKpStGs but with a different cartridge. I want to do this properly but I’m having trouble finding resources on the process. Any help is appreciated.

[running-man]

Pretty interesting read on that reddit post.  That guy has a lot of skills making his own reamer and whatnot.

I would think replacing, sleeving, or adding to a bolt for a different sized case would be pretty straightforward as long as the integrity of the bolt is maintained.  If I was looking at doing something like this, I'd think these would be the options I'd look at:

• Best but probably hardest option would be to manufacture a brand new bolt out of pristine material sized to the cartridge you want to use.  They are relatively straightforward rectangular parts with mostly straight sides and you could use a very strong modern forgiving material like 4130 or 4340 at a (relatively) low hardness to ensure it meets or exceeds the strength of the original.  There are maybe some difficult compound angles to deal with and the firing pin hole through the center might be tough to keep straight based on the length to diameter ratio...
• Least desirable but probably easiest would be to add material where you need to via welding and then hog out what you need to in order to make the new case fit.  I would think the structural integrity of the bolt would be something you would need to keep tabs on.  Would the bolt need to be heat treated to eliminate the heat affected zone at the weld?  Probably a question for a metallurgist.  Also the amount of heat you dump into the weld could do some squirrely things to warp the bolt if things get too hot.
• Option in between would be to mill off the entire bolt face and then ream a very tight hole concentric with the firing pin channel.  You could then make a blank with boss that will heavy press fit into the reamed hole that you could then finish the bolt face as you wish.  This method has the benefit of keeping the parts that interface with the receiver stock and you only have to worry about the fit of the cartridge and headspacing.  Extractor might need to be modified too depending on how similar the cartridge is with 7.62x39.

Sounds like a very neat undertaking.  I'd love to see an SKS in something other than 7.62x39 or 5.56x45.

[theSKSguy45]

The plan was 5.56 because of the availability of AR mag well adaptors and the ability to use pistol mags increasing my capacity from 5 to a whole 10 rounds (thanks Canada). 7.62x39 pistol mags are available but that’s boring. But I figured I’d keep it simple by using a cartridge I actually have a magazine already made for. I can go nuts with something super out there after this project maybe. Although I foresee it being something that happens in a few years because I’d like to do it all in house (literally) and I’ll need to buy a lathe, mill, new welder (mine is a bit jank) and a bunch of other stuff. Just looking for ideas to keep my mind working on it in the meantime. If anyone has pictures of a 5.56 SKS I’d love to see them.

The first two suggestions were what came to mind but I hadn’t considered the third. Interesting, I’ll add it to the idea bucket. Does anyone know what metal was used for the bolt on SKSs? If I would need to heat treated it I’d imagine that would be an important detail

[Greasemonkey]

Be totally different,  go unhinged     do a 6.5 Grendel SKS.. a 6.5x38mm... If it's available in Canada.. it and the x39 base diameter should be close enough to not require bolt machine work, it already fits in the magazine(you can still do the AR mag swap) and it's slightly lower chamber pressure than the 5.56, the 6.5 is closer to the 5.45 round pressure wise, so the gas system and springs could be easier to work with and tune. That, and a 6.5mm flies really nice in distance.

[xtriggerman]

 Shim soldering the bolt face is a basic Gunsmith job all tho I'v never done one. Brownells sells a solder wire that flows at 475% thats cold enough not to disturb the bolts hardness. Boring a new seat deeper into the bolt is not an option since the hardness of the bolt would be removed and you will be into soft metal. also the extractor would need to be made new. again not a good option. Soldering in a shim is pretty straight forward, just fresh rough both areas and tin each separately, flux and then join the 2 with just enough heat to flow the 44 solder. A map gas tank should get you there. Just dont go over 500, at that point you start to change the temper some what. Another issue you might have is hitting a small primer with a large primer Firing pin. That may prove troublesome. Some years ago, there was a vid of a guy soldering a shim on a bolt action bolt face.
https://www.brownells.com/tools-cleaning/general-gunsmith-tools/adhesives-solder/hi-force-44-solder/

[Sindone]

I did a mosin nagant bolt to fit the 8mm cartridge.  I machined down a washer then used silver solder to attach it. 

[xtriggerman]

If that infact is a golden color I see there..... yup you used silver solder all right.  I would caution against firing that bolt head. silver solder will flow in a 1200- 1700 Deg. F.  Basicaly, you annealed the bolt head to soft steel if all you did was soldered it and let it air cool. There is no good way of hardening n heat treating a silver soldered carbon steel part since a hardening quench is at about 1500, as a hard saline or oil quench, then a tempering to anywhere from 450- 650 depending on application. I wouldnt put my eye ball behind your bolt unless it was a 22LR in front of it.. Just sayin......
  Best case scenerio is its soft threw and threw and will just peen its self back untill head space problems begin to appear. Worst case is only the leading bolt face go hot while the body shank stayed cooler. The difference in temps will create differing stress points. If you only water quenched to cool and it sizzeled, it will be prone to crack  under high shock impulse.

[Sindone]

The work piece doesn't get 1200° This bolt was made over 20 years ago.

[theSKSguy45]

Do you have any resources on heat treatment I could look at by chance?

[xtriggerman]

  The most basic gun steel is 4140. Look up Hardening and heat treating 4140. Google gives you a general idea. Of course we dont really know exactly the alloy content of the steel since I have no resource for SKS bolt material that was used. So, to know exactly the proper temps to heat, quench and then treat is a bit of a gamble to get it to duplicate factory hardness. finished hardness should be around the 42 rock well C scale but thats just a guess as well. That would be your target I 'm guessing. I would suggest that if you dont have a rudimentary metallurgist back round that can fill in all the above blanks, dont mess with applying more than 450 Deg. F to anything that must contains 40,000+ psi in front of your head. I hate to rain on anyones parade but if I kept my mouth shut and then some one reading this thinks welding or silver soldering on a bolt willi nilly is safe bubba practice, then loses an eye, shame on me for not voicing a warning. The MOST important part of a hi pressure firearm is the properly harden alloy steels encompassing the horrendous explosion just inches away from your noggin.    Nuf said.

[xtriggerman]

The work piece doesn't get 1200° This bolt was made over 20 years ago.

Please look up what temperature you need to flow silver solder. God forbid, dont take my word for it.

[xtriggerman]

 Gez, If I knew I could have this much fun right off the git go, I'd a checked in sooner! 

[Greasemonkey]

Interesting

Makes me wonder how say... A laser welder, tacking an interference fit sleeve would work, or maybe a really good TIG, again just tacking two or three spots.  Would tacking be sufficient and or would that alter the metal hardness other than in the localized spot welded area vs the mentioned solder method.

Another idea I wondered about.. an interference fit sleeve pressed in and pinned, and possibly with strong bearing retaining compound..

Retaining compound is the devil in my field,  works great till you have to pull it apart years later.

[theSKSguy45]

Hey figured I’d post an update to this. I ended up going the route xtriggerman had suggested and sleeved the bolt. I changed the cartridge from 5.56 to 7.62x25 as I already have a barrel that will work with that cartridge and I have a bunch of Ppsh mags lying around. The build is progressing at a reasonable pace but I’ll post the full version in a seperate thread.

Turning the OD to the correct dimensions (with the good ole drill and file trick as I still don’t have a lathe)

Pressed into place. Looks good

Did my best to keep it under 500 but I saw some golden colour on the bolt afterwards. Being 7.62x25 I’m not too concerned but it’s definitely good to know for future reference.

Filed to shape

Test fit with a round of 7.62x25. Fits perfectly

And here is the result. Probably doing the magwell mods next as that’s going to determine how I go about the rest of the build. Debating on trying to keep it a locking action or just saying **** it and going direct blow back. Will update with progress pics at a later date.

[Worm]

Dude this is wild haha can’t wait to see how she turns out! Well done