Best length barrel for 7.62x39?

[osiris32]

Does anyone know what would be the best length barrel for the 7.62x39 cartridge? This is for an AR project and yes I know the implications of this cartridge in this platform.

[The_Hammer_Man]

Originally Posted by osiris32

Does anyone know what would be the best length barrel for the 7.62x39 cartridge? This is for an AR project and yes I know the implications of this cartridge in this platform.

I've built several different 7.62x39 uppers for customers and the general consensus appears to be eighteen inchs as the "default" barrel length for accuracy.

For speed/time on target/CQB the 12.5" is very popular.

With that said,, I've seen 7.62 uppers in all lengths... from 10.5" up to 24". So IMHO barrel length is "mission driven" when making a decision.

Figure out what youre going to use it for then choose accordingly.

[osiris32]

18" sounds good, not really looking for a CQB rifle in the caliber. Thanks!

[IrishDevil]

If I'm not mistaken I believe 7.62x39 was developed with a 16" barrel in mind. Hence most AK's have 16" barrels, take that for what it's worth though.

[mbogo]

'Best length' in terms of what? Velocity? Handling? Efficiency?

mbogo

[The_Hammer_Man]

The "best" rule of thumb I've been able to come up with over the years of fiddling with this and other calibers is twist rate vs barrel length.

Granted, I am not an engineer so, if I've made a mistake in my thinking PLEASE correct me!

Step1) Measure case length ... lets use a nice easy number... two (2) inchs.

Step2) Add that two (2) inchs to your twist . Let's use 1:10 since we're talking about 7.62x39. This would mean to get at least one full twist to stabilize the bullet we'd need a barrel twelve and a half (12.5") long.

Step3) Remembering that barrel length helps muzzle velocity and muzzle velocity is one of the determining factors in terminal ballistics.

With it's relatively low muzzle speed/energy the 7.62x39 truly benefits from longer barrels. Which might be one of the reasons the RPK/RPD type rifles have 22" and 24" barrels.

YMWV depending on twist rate and barrel length... also who made the barrel.

Choose wisely.

[LMTRocks]

I've got two ARs in 7.62x39 and they both function very well. I did have to make some M4 ramp adjustments when the 2nd upper I built didn't have a barrel extension that matched perfectly with my upper receiver's M4 cuts. My 16" rifle is scoped and lives on a SOPMOD equipped lower. The recoil of the weapon is negligible. It prints about 4moa at 100yd with my Leupy Rifleman scope using Yugoslavian Milsurp ammo (M67). I also have a 10.5" AR Pistol that sends 123gr rounds downrange at around 2100fps. The beauty of the .30cal bore is that it loses less velocity than a 5.56 because the volume of the barrel is larger. It isn't extremely loud, but I do plan on getting a suppressor for it next year. The M4 ramps on it also run well and I use 26rd Grendel magazines loaded to 20rds. BTW, the gas port is .093---around 3/32 and it runs like a sewing machine

[mbogo]

Originally Posted by LMTRocks

...using Yugoslavian Milsurp ammo (M67).

Is this ammunition corrosive? I am intrigued at the idea of a 7.62x39 AR, but have concerns about damage to the gas system (and other internals) when using foreign milsurp ammunition.

Thanks,
mbogo

[Clint]

Originally Posted by osiris32

Does anyone know what would be the best length barrel for the 7.62x39 cartridge? This is for an AR project and yes I know the implications of this cartridge in this platform.

What length? What are your needs?


x39 retains excellent velocity in short barrel applications

123 grain projectile goes
2400 from 20"
2350 from 16"
2250 from 12.5"
2100 from 10.5" (as previously stated )
2000 from 9"

The other interesting 30 cal option is the 300 BLK

[osiris32]

Originally Posted by Clint

What length? What are your needs?


x39 retains excellent velocity in short barrel applications

123 grain projectile goes
2400 from 20"
2350 from 16"
2250 from 12.5"
2100 from 10.5" (as previously stated )
2000 from 9"

The other interesting 30 cal option is the 300 BLK

Interesting that there is not much velocity gain by 4" of barrel. Thanks for the information. Do you know who makes good 16" 7.62x39 barrels? Looking at Model 1 Sales.

[SethB]

I don't know where the idea that you need a full twist to stabilize a bullet comes from.

.45 ACP and .22 LR both use a 1:16 twist, but I use them in five inch barrels all the time.

ETA: I would use 16 inches for hunting and 12 for fighting.

[constructor]

We run 16" with a mid gas system, it allows the pressure to drop so the steel cases aren't stuck to the chamber walls when the extractor starts pulling them from the chamber. As long as they aren't over-gassed it shouldn't be a problem but, many are over-gassed.

[LMTRocks]

Originally Posted by mbogo

Is this ammunition corrosive? I am intrigued at the idea of a 7.62x39 AR, but have concerns about damage to the gas system (and other internals) when using foreign milsurp ammunition.

Thanks,
mbogo

After shooting this stuff since about march and taking the 16" upper apart I can attest to no gas system issues. The bolt does get a little "red" from the corrosive primers but that is quickly solved with Gun Scrubber and a brush after some range time. I also use it when I just want some blasting fun with my AR pistol. Both barrels look very good for the amount of shooting I've done with them this year. Just don't let the BCG stay dirty for a long time. Always hit it with some Gun Scrubber before you leave the range or go to bed.

[308sako]

Colt 16" shoots 165's at 2,000, 155's at 2150, 125's at 2350. Kills deer DRT

[OhThatGuy]

So an AK in 7.62X39 with a 14.5" rifled barrel and pinned muzzle brake will have nearly the same velocity as a 16" barrel? That is good stuff.