I saw a video that stated that .300 Blk round are routinely loaded with pistol powder. I took this to mean supersonic loads included. It stated that the powder was completely burned in the first 9" of barrel, so longer barrels are irrelevant, at least from a velocity standpoint. Is this true?
If so, why bother getting a full length (16") barrel AR? On the flip side, does any major company load .300 BLK with rifle powder specifically for longer barreled guns?
And does this make it a better round for shorter barreled ARs?