One of the reasons I am considering .300 AAC is a published Alliant 2400 loading using 16+ grains to push a cast .308 gas checked round. VERY similar to a .311 gc round I load for my SKS. While I don't get into the 16's, I do exede the 14.5 published for 7.62x39 (and you can find anonymous 16 grain x39 loads online so I know I am not too far off the reservation). @2300 fps or therabouts its a LARGE load of pistol powder (I load a 158 grain gas checked lead RF .358 with 15.2 grains of 2400 for .357 rem mag). Subsonic doesn't interest me. If zombies are attacking the house. I want EVERYONE around to hear the defensive fire. (And the zombies know where the fire is coming from anyway.)

Looks to me that the difference between weight AR-15/AR-10 based MSR is 7 vs 10 pounds give or take. And the extra range of 7.62x51 is of no benefit.

According to GunData.org the velocity and trajectory of a 123 grain 7.62x39 FMJ and a .30-30 150 grain JSP is IDENTICAL through 0-250 yards. Probably within the variation between lots of ammunition. That is my experience with 155 grain cast .311 and 180 grain cast .308 out of a 16.25" SKS and a 16.5" Marlin 336. IDENTICAL, (.30-30 probably has a bit more top end potential).

If one was to build a x39 AR, I assume some bolts are better than others.

Does anyone have first hand experience of cycling issues with SUPERSONIC .300 AAC in 16" barrel with a carbine length gas system.

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