300 AAC BLACKOUT 12.5 inch = 300 Fireball 16 inch?

[rsilvers]

It is looking like a 12.5 inch 300 AAC BLACKOUT matches the velocity of a 16 inch 300 Fireball. This is probably due to the extra freebore (like 5.56mm compared to 223 or 6.8 SPC-II compared to 6.8 SPC SAAMI).

I was noticing that I could extra grains of powder before signs of pressure in a load that others were using with 18 grains. Previous loads will need to be re-worked up if you have a real 300 AAC BLACKOUT chamber. And remember - don't shoot 300 AAC BLACKOUT ammo in a previous chamber as it will have additional pressure.