BARREL HARMONICS

[echo1]

Hi All,

When shooting my Paratrooper, it's generally the more accurate, or consistent on paper at the 100 yard range, than standard 20" barrels, and having recently built A short barrel home grown clone, I'm expecting similar performance (yet to shoot). I've heard tell that SKSs were "zeroed" with the bayo fixed, and group better with the bayo extended. I myself, have bayos on all my rifles, but I've never shot with fixed bayonets, to see for myself.

I've also heard more than one M59/66 shooter, whom own other SKSs flavors, say the Yugos with the GL are their most accurate. Although I don't recall if that was with the bayo or not.

On my next butcher job, I was considering using one of these 2 types of threaded brakes, on a rifle with no FSB, and possibly cutting the barrel some. I know 2-3 hundred yards is the operational range for the cartridge and platform at the 20" length, despite weeb tales of greater distances. Any opinions or experience with optimum barrel lengths/brake combinations to still range out a couple hundred yards?

I've seen slo-mo of a T56 SKS firing, and was quite surprised how much whip there is. If the GL on a Yugo is part of the equation for better grouping, might one of these brake be effective. I know it could be a combination of everything hanging off the front of a M59/66 (GL, collar, ladder sight, bayo), that some how aids in suppressing, influencing, or controlling, the harmonics. Like a strut on a Mini 14. PAX

[Phosphorus32]

First, I'll start off by saying I have no experience with changing the barrel length on an SKS.   

Barrel harmonics are rather complicated. The simplest case is a scoped bench rest bolt action rifle with a free floated barrel of a uniform thickness with no front sight. I think the main harmonic wave is an annular wave from expansion/contraction of the chamber that is transmitted down the barrel, but there are undoubtedly other forces at work from the gas and bullet travel down the barrel and departure at the muzzle under ways affected by the attachment and configuration of a muzzle brake, for example.  A complicated case, like the SKS, with contact points along the barrel and a mass of asymmetrical proportions at the end of the barrel undoubtedly makes the harmonics very noisy and complicated. 

It's fun to understand and contemplate the physics.  Is your barrel cut to the right length to work with (constructive interference) or against (destructive interference) the harmonics? Does the mass at the end dampen (absorb) the harmonic wave? Does it change the frequency and/or amplitude and return a weaker (lower amplitude) secondary wave in phase (no change in frequency) or out of phase (change in frequency) with the primary wave?  Are the powder burn rates and total charge chosen correct for your rifle? 

The questions are so complicated that I think everyone tunes barrel harmonics by trial and error.  It seems most people cut and thread and attach and then work up loads to obtain the best results with the complicated equation (rifle) they end up with.

[Greasemonkey]

No clue about bayonets on SKSs, on Mosins, they do effect POI slightly, some more than others. Now, I cant say is its a vibration thing, or because the gases exiting the barrel reflects off the bayonet and possibly pushes slightly on the bullet. Honestly, I did it for grins and giggles once, normally I just don't fire them with the bayonet extended.

Now whats going to move faster, the harmonic wave or the bullet. From the time the bullet first moves to muzzle exit maybe .8 to 1.5 ms will pass. One reason bolt actions have the advantage in accuracy, alot of the lock time and crap in between is removed, you have a simple trigger and a sear, there is less time for error. Maybe simplifying the trigger group would yield results as much as attachments to the barrel.

Then one has to take in to account heat, expansion of gas system parts, barrel warp as temperature changes, all that will slightly change the harmonics simply because tolerances change with heat.

I can see a short barrel being of some benefit, it might be slightly stiffer, but at the same time wouldn't a thicker, longer barrel gain the same. This method eliminates the gas system and uses a thicker heavier barrel.
http://sks-files.com/index.php?topic=130.0

Me, I'm trifling, I'll just go get my K31 or M39, I have absolutely no doubt about their proven ability at 2-300 and beyond yards. 

[echo1]

First, I'll start off by saying I have no experience with changing the barrel length on an SKS.   

Barrel harmonics are rather complicated. The simplest case is a scoped bench rest bolt action rifle with a free floated barrel of a uniform thickness with no front sight. I think the main harmonic wave is an annular wave from expansion/contraction of the chamber that is transmitted down the barrel, but there are undoubtedly other forces at work from the gas and bullet travel down the barrel and departure at the muzzle under ways affected by the attachment and configuration of a muzzle brake, for example.  A complicated case, like the SKS, with contact points along the barrel and a mass of asymmetrical proportions at the end of the barrel undoubtedly makes the harmonics very noisy and complicated. 

It's fun to understand and contemplate the physics.  Is your barrel cut to the right length to work with (constructive interference) or against (destructive interference) the harmonics? Does the mass at the end dampen (absorb) the harmonic wave? Does it change the frequency and/or amplitude and return a weaker (lower amplitude) secondary wave in phase (no change in frequency) or out of phase (change in frequency) with the primary wave?  Are the powder burn rates and total charge chosen correct for your rifle? 

The questions are so complicated that I think everyone tunes barrel harmonics by trial and error.  It seems most people cut and thread and attach and then work up loads to obtain the best results with the complicated equation (rifle) they end up with.

I know that there's a lot of math and physics involved. I was just wondering if any had some practical field experience. The brake will mainly contribute to faster follow up in a string, but I was curious how it may influence grouping from a bench. PAX

[Dannyboy53]

Echo1 some time back my wife tried this with her Chinese carbine with these results:



 Re: My other /26\ Chinese SKS
« Reply #24 on: October 08, 2014, 01:31:04 PM »


Quote from: running-man on September 24, 2014, 04:45:02 PM
110% improvement there Danny!  When you shoot it next, you might try extending the bayo and see how that affects your accuracy.  Some people swear there's an improvement with the bayo extended.




Running-man since you posted this statement we recently did some shooting and Mary decided to try extending the bayonet for the heck of it (I thought you were joking about this!) and see if it had any effect on the groups. I read statements pro and con and to be honest I am a bit skeptical!

After firing a few shots with the spike bayonet stowed away Mary extended the bayo and fired a few more rounds from her [0306] gun and the group tightened up from about 2½" to about 1¼" at 25 meters. I was surprised and quite frankly thought it simply a stroke of good luck but she got the same results a second time!

[Power Surge]

This is something I have experience with, both from my benchrest .22 shooting and actually trying stuff with SKSs.

The short answer is.... there is no one answer.

When you fire a bullet, the barrel flexes up and down, in a motion similar to waves on the ocean. And since it's flexing up and down, that means the muzzle end where the bullet comes out as well. So sometimes the end of the barrel is flexing up and sometimes it's flexing down.

With that said... where the barrel is at the point of bullet exit, is what dictates where the bullet will go. Sometimes bias upward, sometimes bias downward. Barrel TUNING, is when you makes changes on the gun, to make the bullet exit the barrel on the same exact "wave" every time. So if your bullet leaves the barrel on the up wave of the muzzle every time, you get tighter groups and better accuracy. Barrel tuning is generally achieved with a barrel tuner. This is a device that goes onto the end of the barrel and alters the wave pattern to be consistent. Some tuners are adjustable, and some are solid, calculated of complex formulas. Barrel tuning is definitely a science.

But when it comes down to it, a barrel tuner is simply a weighted device on the end of the barrel. So, ANYTHING hanging off the muzzle can change the dynamic. An extended bayo, a muzzle brake, a silencer....anything can affect it. Sometimes it helps, and sometimes it hurts. In the case of the SKS, I have had my groups shrink in half with the bayo extended on some guns, and grow twice the size on others.

And, there are other variables too that affect tuning. Especially ammo. The pressure wave from the explosion of firing a round is what transmits through the barrel. And the weight of the bullet itself will change at what point it exits the muzzle too. This will change with every shot when using run of the mill ammo. Because powder charges and bullet weights are not exact from round to round. That's why hard core target shooters use "match ammo". Match ammo is ammo where every round is made virtually identical for maximum consistency.

So what does this all mean? It means every gun will be different. There's no definitive answer. You just have to do some trial and error with each specific gun you have and see how it reacts.

[Dannyboy53]

I'm beginning to understand why my shooting is so bad. Sometimes my rifle muzzle is jumping all over the dang place even when I don't squeeze the trigger.