Thread: got some range time with the 8mm and 7.62x39

I was reading somewhere (not sure if it was here?) that the Soviets made their 7.62x39 barrels using the same tooling as they made their Mosin / PK barrels with - with 54r needing a fast twist rate for the much longer and heavier projectiles it's lobbing. So AK's got the same 1 in 9.something and this legacy has carried on for no apparent reason in modern guns. It's overly fast for x39's lightweight bullets which can be quite detrimental to accuracy.

So yeah, 150's should shoot better, although they're a bit pedestrian.

Originally Posted by PommyMcPomFace

I was reading somewhere (not sure if it was here?) that the Soviets made their 7.62x39 barrels using the same tooling as they made their Mosin / PK barrels with - with 54r needing a fast twist rate for the much longer and heavier projectiles it's lobbing. So AK's got the same 1 in 9.something and this legacy has carried on for no apparent reason in modern guns. It's overly fast for x39's lightweight bullets which can be quite detrimental to accuracy.

So yeah, 150's should shoot better, although they're a bit pedestrian.

On this forum. A 7.62x39 would be fun to experiment with using heavy round nose cast bullets. The smaller case disadvantage would be partially cancelled out by the fact that a lead boolit of same weight as a jacketed requires a third less powder to achieve the same velocity. And like you say, theoretically it should fly more accurately with the fast twist. Just out of interest, @PommyMcPomFace, how many grains of H414 do you reckon you can load into a 7.62x39 case? (-:

Originally Posted by Cordite

Worth stressing that a 170 grains heavier boolit does not necessarily equate to bigger recoil. Cast non-jacketed bullets require a third less powder charge for same velocity, and the velocity run at is lower in any case (because of limitations of the strength of lead vs rifling grooves). As shooternz points out, cast HP boolits are good (better) at expanding, even at quite slowish velocities.

As an aside (I initially misread the post, thinking someone was considering heavy boolits in an 7.62 Soviet rifle). Heavy boolits in a 7.62x39 rifle. When the 7.62x39 round was adopted by the Soviets in the 1940s, they went for a 1:9.45" twist which was copied straight from the 7.62x54R Mosin rifle. Same rifling machines making different / same-same barrels. This fast twist was originally adopted to stabilise heavy 210 grain round nosed projectiles, but reincarnated in the x39s spinning 126 grain bullets it is just too fast - actually deleterious to accuracy, so some modern manufacturers offer 7.62x39's with slower twist rifling for that reason.
The traditional 7.62x39 barrel has an inherited/throwback ability to stabilise heavy, long slugs with a fast twist it has no need for with standard milspec ammo (except perhaps for longer tracer bullets). A heavier bullet will do just fine in the standard 7.62x39 fast twist barrel, in fact it will feel strangely and unexpectely at home with a just fine twist rate.