I will be attending SHOT in a couple of weeks and I plan on speaking with SilencerCo and Advanced Armament Corp. regarding the rifling profiles for their threaded replacement barrels.
Another interesting tidbit about 300BLK, I've heard that it's possible to use projectiles meant for the .308 WIN cartridge for handloading 300BLK.
I've been a fan of 300BLK since it was introduced and I'm definitely going to build at least one gun chambered for that cartridge.