Scenario: You own AR-15s both in the standard 5.56 NATO chambering and in .300 Blackout. You get to the range one day with your 5.56 rifle and discover - oh no! - you accidentally grabbed your 300 BLK magazines. You don't want to drive all the way home if you don't have to. The .300 Blackout cartridge uses a 5.56 NATO case necked up to hold a .30 caliber bullet, so can you use .300 Blackout magazines in a 5.56 / .223 rifle? How much of a difference is there between them? Compare the front lip of the mag body and the guides just under the feed lips of the two magazines, says Brownells Gun Tech™ Caleb Savant. "Ogive me a mag with a little extra clearance for the larger .300 Blackout bullets," he sings. (Actually, he doesn't, but you get the point.) In most cases, you CAN use the Blackout mags in your 5.56 / .223 rifle - with a. caveat that Caleb explains for us.
