The 300 AAC BLACKOUT throat is such that a 220 Sierra MK loaded to 2.26 OAL will have a 0.010 jump to the lands.
Here is an FAQ:
http://www.silencertalk.com/forum/viewtopic.php?f=128&t=73274&p=699521&hilit=faq#p699521
Here is an FAQ:
http://www.silencertalk.com/forum/viewtopic.php?f=128&t=73274&p=699521&hilit=faq#p699521