Quote History Originally Posted By Brazos_Jack:

I think magazine length will be your greatest hurdle. The x39 case is alot longer than the Blackout case. The AK mag is around .100" shorter than an AR mag. So you'll be able to use longer bullets in the AR. Still, you can only seat as deep as where the ogive starts. Look for the longest, heaviest bullet whose nose section beyond the full diameter shank is less than .770" long.



I believe that the reason for the fast twist was a desire to use the same rifling equipment as the Mosin Nagant, which originally needed the fast twist for its original 210 gr bullet. View Quote View All Quotes View All Quotes Quote History Originally Posted By Brazos_Jack:

Originally Posted By towerofpower94:

When time allows I'm going to try and work down to a subsonic load with AA1680 and the 200gr Lapua D166. I believe this is the heaviest bullet available in the .310-.312 class and am hoping the load will eventually be something similar to a 300BO with ~200gr bullets.



Whether the final 1,000fps load will cycle an AK-103 or AK-104 clone or my 7" AR upper will remain to be seen.



ETA: as to your original question of why did the Russians keep the fast twist rate...could it be akin to our military using the faster twist rate to ensure stability with the "long for weight" tracer bullets? I've no experience taking apart and measuring/weighing a Russian tracer round, but this might be a real world reason for why they kept the sub-optimal twist rate for the stubby 123gr FMJ bullets.



I believe that the reason for the fast twist was a desire to use the same rifling equipment as the Mosin Nagant, which originally needed the fast twist for its original 210 gr bullet. I think magazine length will be your greatest hurdle. The x39 case is alot longer than the Blackout case. The AK mag is around .100" shorter than an AR mag. So you'll be able to use longer bullets in the AR. Still, you can only seat as deep as where the ogive starts. Look for the longest, heaviest bullet whose nose section beyond the full diameter shank is less than .770" long.I believe that the reason for the fast twist was a desire to use the same rifling equipment as the Mosin Nagant, which originally needed the fast twist for its original 210 gr bullet.



While on the surface it might seem that simple, I find it unlikely a nation which decided to undertake the army-wide manufacture of a a very different rifle would cut corners when it comes to rifling "because we already have machines that do that twist rate".



I mean, it's not like they just took the Mosin or SVT-40 barrel and chopped it here and there to make it fit an AK47 front trunnion.



You may very well be right, but I find it unlikely that an entirely brand new rifle design would skimp on what is arguably one of the most important parts, especially since they went from MK's stamped receiver design to a milled receiver for the type 1-3 rifles once they figured out their sheet metal production and stamping processes were not up to the specs needed to achieve his initial design. While your twist rate:bullet weight:cartridge comparison in the OP is an awesome reference, it doesn't mean your 'belief' and MK's decision making process are congruent, haha.While on the surface it might seem that simple, I find it unlikely a nation which decided to undertake the army-wide manufacture of a a very different rifle would cut corners when it comes to rifling "because we already have machines that do that twist rate".I mean, it's not like they just took the Mosin or SVT-40 barrel and chopped it here and there to make it fit an AK47 front trunnion.You may very well be right, but I find it unlikely that an entirely brand new rifle design would skimp on what is arguably one of the most important parts, especially since they went from MK's stamped receiver design to a milled receiver for the type 1-3 rifles once they figured out their sheet metal production and stamping processes were not up to the specs needed to achieve his initial design.