The bullet of a subsonic cartridge can be any size. In the case of .300BLK, they both used a larger bullet (220 or 240gr, usually) but also a reduced powder charge (usually around 9gr, compared to the ...

Correct me if I'm going it at wrong and I know it's a minor detail in a pretty lengthy and great article, but don't gun propellants undergo deflagration rather than detonation when they combust, well ...