I wrote in November about a friend who survived firing a .300 Blackout cartridge in a .223 barreled AR-15. The resulting detonation wasn’t pretty.

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Our own Tom McHale witnessed a very similar AR-15 kaboom today, in person:

I’ve read a few stories recently about someone, somewhere, shoving a 300 AAC Blackout cartridge into a .223 / 5.56mm rifle and pulling the trigger – subsequently blowing their gun to bits. Some folks call BS and say it can’t happen as the rifle won’t go into battery and fire.

Well, I’m a believer now, considering a guy 3 lanes down from me blew up his fairly nice looking AR today. In the confusion, I was not able to get the brand of the rifle, but that matters little. Containing 55,000 pounds per square inch of pressure is not in the job description.

Tom’s description of the rifle, magazine, and shooter eerily echo that of other 300 BLK/.223 kabooms I’ve heard of, and in each instance, it appears that lighter .300 BLK bullets can be chambered just enough for a firearm to fire, especially with handloads that might not be seated at the correct depth.

To date, I’ve been unaware of anyone being seriously injured or killed in a .300 BLK/.223 kaboom. I hope that luck holds.

If you own both calibers, please be very careful about segregating your ammunition. I don’t want any of you hurt.