5.56x45mm VS. .223 Remington

What?  Aren’t these two rounds the same?  Well, yes and no.  If you look at the case dimensions, they are identical in every way.  Right down to the angle of the shoulders.  However, aside from that, the differences are quite remarkable.  Let’s dive right into them, shall we?

First of all, 5.56mm brass will tend to be thicker than .223 brass.  Why?  Because NATO rounds are loaded to much higher pressures than civilian rounds.  For instance, NATO rounds are loaded to over 62,000 psi while .223 rounds measure around 55,000 psi.  That’s a pretty big difference.

Second, the leade is longer in 5.56mm chambers, and they are proof tested to take the higher pressure of the NATO round.  The leade is the measurement of the distance between the mouth of the cartridge and the point where the bullet engages the rifling.  .223 chambers have shorter leades and are proof tested to the lower SAAMI pressures.

So does that mean I can’t fire 5.56mm in chambers rated for only .223?  Technically, you can, but there is a big caveat.  Because the case dimensions are identical, a 5.56mm round will chamber and fire in a .223 rifle.  However, you run the risk of serious damage to your rifle, and major injury to yourself if you do so.  Rifles chambered for 5.56mm can safely fire .223 Remington ammunition safely, but it won’t be as accurate.

The differences are not limited to the chambers, but also to other parts of the rifle.  For instance, in an AR both the upper and lowers would need to be rated for 5.56mm and not .223 Remington only.  The only way to be sure is to read the owners manual to make sure that your rifle is rated for 5.56x45mm pressures to avoid undue wear and stress on your firearm.

Most new rifles (particularly Black Rifles) are all chambered for 5.56x45mm.  In fact, you might find it difficult to find an AR chambered in .223 Remington only.  For those of you who are interested in building an AR from a kit, I know for sure that the Del-Ton kits are chambered for 5.56x45mm, so there are no worries there.

Bottom line, you can fire 5.56x45mm in a rifle chambered for .223 Remington, but it isn’t a good idea.  No matter what the situation is, you always want to stay safe when shooting a firearm.  Whether target shooting, or self defense, the idea is to inflict more damage on your target than on yourself.