Written by Sierra Bullets Chief Ballistician Tommy Todd
In the firearm industry there are several scenarios where a person can chamber a cartridge that is not correct for the gun being utilized. This can cause a catastrophic pressure event and damage when fired, usually affecting both the gun and the shooter. A classic example of this scenario is mistakenly loading a 20 gauge shotshell in a 12 gauge chamber. The ammunition chambers easily and will usually slide into the bore, but fails to fire, creating an obstruction. The shooter then chambers a 12 gauge shell behind it and fires the gun, the bore obstruction causing extreme pressure to build and damage to the gun and shooter.
Due to the popularity of the 5.56/223 Remington cartridge and the recent popularity of the 300 AAC Blackout cartridge, there are many shooters that own both chamberings. There have been several instances of a 300 AAC Blackout cartridge being chambered in a 223/5.56 firearm, and then being fired, resulting in a high-pressure event. Upon investigating the possibility of this, I found that for the Blackout cartridge to fully enter the 5.56/223 chamber, the bullet must be pushed deeper into the case than the original factory length. One can search the internet and find instances of this event having occurred and pictures usually reveal both broken gun parts and bodily injury. While attending the SHOT Show last month, I visited with a gentleman that had worked on an AR-15 chambered in 5.56 that had a 300 AAC cartridge fired in it. The 125 grain bullet (#2121) was lodged in the barrel (pictured below). The gentleman was able to push it out with a cleaning rod, and luckily in this instance, the shooter was not seriously injured.
As firearm owners, we are constantly aware of (and being reminded), that we must be vigilant in regards to safety. A large part of firearm safety is to ensure that the ammunition is correct for the firearm being utilized. There are many ways of ensuring proper ammunition/firearm use, including color coding ammo boxes, magazines, labeling, separate storage, etc. Whatever method you choose that works best for you, please remember to always double-check as the consequences can be costly.