Longer barrel on a 7.62x39?

[Hammerhead6814]

I was reading sksboards a little while ago and ran across a thread inquiring about longer barrels on a 7.62x39 gun. The idea behind a long barrel is that the powder has more time to burn and therefor the projectile will gain more kinetic energy (well he didn't say it like that, but same idea).

The question I guess is: would a barrel longer than 20 inches give the 7.62x39 cartridge better ballistics at 150 to 200 meters? I'm interested in this because I've got a SKS that I'd love to try and make a 200 meter rifle, and heck if a $100 barrel (or however much they run) is all that stands in the way, then maybe it's something I'd give a try?

 

[dscottw88]

Almost all projectiles (including the 7.62x39) will gain velocity when the barrel length is increased. However, a round such as the 7.62x39 won't utililize this extra length well enough to make using a shorter barrel a concern. This doesn't mean it wont help at all, quite the contrary, I'm sure it will help alleviate some bullet drop that the round is known for. Its only really viable out to 400 yards generally.

In short, yes, a longer barrel will not only increase velocity, but will also increase lethality. Although I can't say I recommend swapping barrels on a SKS. Most come with 19" barrels anyways. Only a few (ex: Chinese paratrooper model) come with 16" barrels.

 

[praharin]

Can't a barrel that is too long actually decrease velocity?

I'm not really all that savvy on the internal ballistics, but it would seem that once all the powder was burned, any more barrel would only cause drag.

It's something to think about anyway.

 

[R.W.Dale]

Can't a barrel that is too long actually decrease velocity?

I'm not really all that savvy on the internal ballistics, but it would seem that once all the powder was burned, any more barrel would only cause drag.

It's something to think about anyway.

in theory YES...BUT with most centerfire rifle the calculations put the point of no gain at somewhere around 40"


As to the OP's question see sig link number 3 for 7.62x39 ammunition tested in barrels ranging from 16 to 26 inches

? I'm interested in this because I've got a SKS that I'd love to try and make a 200 meter rifle, and heck if a $100 barrel (or however much they run) is all that stands in the way, then maybe it's something I'd give a try?

even in a 20" tube 7.62x39 is much much more effective than internet armchair ballisticians give credit it for. See sig link number 1

 

[Deus Machina]

I never see anyone cracking on x39 say anything bad about .30-30, which is almost-but-not-quite ballistically identical.

The truth about x39 is that, for every purpose it was ever meant to do, 16" is perfectly fine, 20" is just dandy, and up to 24" will be grand if cumbersome.

If you need more than the gain 24" will get you over 16" or 18", you need to be using something stouter than an intermediate round anyway. Further out than a 7.62x39 will easily work for, and you need to look into x54R or .308, which will have a comfortable working range further out.

 

[Hammerhead6814]

Thanks Krochus! The 26 inch barrel seems to universally offer around 200 fps more.

If I can find a .312" barrel (apparently that's the true diameter of this thing), I'll give that a try.

 

[rangerruck]

there are a few dudes here, who have done it, and there is also a guy over at RFC, that does custom stub bll/thread jobs to nef/H&R's, that has done a custom job on a x39. plus I think there is a combloc squad rifle weapon, with bipod, that has about a 24 inch bbl on it. Hungarian or Yugo, or some such country; very much like a PSL.

 

[Z-Michigan]

With typical 123gr combloc loads, going from 16" to 20" adds about 100fps, and going from 20" (SKS) to 23" (most RPKs) adds almost nothing.

Edit: I just read Krochus' linked ballistics testing. I do not intend to contradict that which I'm sure is accurate for the tested loads/rifles, and mostly matches my statement about 16" vs. 20". For 23" RPK barrels, I'm basing the statement on lots of other data I've seen, but not personal testing. Since I have a chrono sitting around, maybe I will test 16" vs. 23" at some point and report back - but it will be with Wolf, Wolf MC and/or Golden Tiger ammo since that's my selection.

 

[sarduy]

get a saiga 20'' barrel in .308 and you're all set

 

[starkadder]

I don't read all of the ballistics reports out there, for the simple fact that you can find a huge curve of data and I don't have that much spare time.
But I can tell you from direct experience that my 10AESB RPK with it's 23" heavy barrel, and 2.5-10X40 Swift scope will shoot circles around my other standard AK's out to 200 yards with Monarch 123gr FMJ and will shoot decent groups at 300 yards (lucky to even hit the paper with the other AK's at that range) But thats just my own experience.


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