What ammo does your gun take? Normally, whatever the data stamp on the gun barrel is the ammo you are supposed to use. Match that info against the head stamp of the ammunition, and you're good to go. Mismatches can lead to catastrophe. But why?
Ammunition is supposed to fit inside the chamber of your gun's barrel like a glove. This is easily seen in the photo above. It shows a barrel, unscrewed from the receiver of the gun, cut away to show the chamber. In the chamber is sitting a cartridge that the barrel is meant to fire.
Notice how the cartridge sits in the chamber without any gap, save for a very tiny space just in front of the mouth of the brass case, to leave room for expansion of the brass, due to the enormous pressures created when firing the gun.
Contrast that with the picture below.
In this photo, an AR-15 barrel has been cut away to show a potentially deadly situation in the making.
The most common chambering for the AR-15 is in .223 Remington/5.56x45 mm. But due to the modular nature of the AR-15 design, you can change calibres by changing barrels and other parts, such as the bolt and bolt carrier, which can save a shooter from buying a new gun for every calibre that they want to shoot.
The .300 Blackout is fairly popular for this reason, as it was designed to be used on the AR-15 platform with only the barrel needing to be changed. The bolt, bolt carrier and magazine can all be re-used as the cartridge rim and over-all length is the same as the .223 Remington.
But, the .300 Blackout uses a .30 calibre bullet, and as you can see, it aint'a gonna fit in that .223 hole in the barrel. This cartridge will go off if you pull the trigger, and you will then have a life-altering KABOOM, as we say in the biz.
Have a look at this picture:
Considering your face is just a few inches behind that hand-grenade formerly known as an AR-15 receiver, would you say it's a good idea to make sure you haven't mixed a .300 Blackout cartridge in with the bag of .223 Remington? Yeah, me too.
Check your ammo. It takes a second, and is pretty cheap insurance against turning your gun into a grenade... 🙂