Friday, June 15, 2012

223/5.56

A friend of mine asked me for some help the other day concerning cartridges that were hard to extract and showing other pressure problems like flattened primers, even a pierced primer. He was shooting new factory ammo out of an older bolt rifle that he'd just bought. I told him to bring me a bunch of the brass, even the ones that showed no pressure signs. When I got them I knew right away what it was.
"You're shooting 5.56 out of a rifle chambered for 223."
He looked at me like I was stupid. "They're the same, one's just metric because it's a NATO round."
"Who told you that?"
"Everybody knows that" he said, apparently still wondering if I was fucking with him or not.
"Look, the bullet is the same but the cases are slightly different. The case thickness at the neck of a 5.56 is .002" thicker than a 223 and the headspacing as well as the throat on a 223 rifle is different than on a 5.56 rifle. And on top of all that, the 5.56 is loaded to just a little higher pressure that really ain't that big a deal until you figure in the headspacing and shorter throat in the 223. That's what's giving you your pressure problems. That's really only a big deal in older rifles - most of the newer ones accept both, but not the older ones."
He wandered off and I still think he doesn't believe me.
Now, after all that, I have never in my entire life heard of a 223 rifle blowing up or even being damaged by firing 5.56 out of it but as a reloader, if I were to see those signs on my loads, I'd be backing that fucking powder charge down. That shit ain't healthy.

9 comments:

dhanna59 said...

Spot on Kenny, you are absolutely correct in your diagnosis!

drjim said...

Guys like you make me realize how much stuff I DON'T know!

wirecutter said...

Don't trip, Jim. Most people don't know that and unless you're shooting an older bolt gun with tight headspacing, it ain't nothing to be concerned about.

drjim said...

Thanks, but I still have a lot to learn.
I *finally* started to understand headspacing after I read all the books I bought about the M1 Garand. Since I'll be getting one soon, I wanted to understand all the nuts-and-bolts of it before I got one.
Now that the CMP is selling them chambered in 308, I'm just about ready to order mine.

Anonymous said...

Hey just remember, when you give someone advise that they asked for, because its on a subject you know something about, but what you tell them doesn't fit with what they want to hear..... the definition of crazy is trying to fix stupid....and I aint crazy man.

Riley

Oswald Bastable said...

Of course a quick google would confirm one of you was right and it ain't him!

AM said...

The headspacing probably isn't the issue, the tolerances for both chambers overlap significantly and the external dimensions of the cartridges fall under that overlap if everything is within spec. The real issue is the throat, the closer to the lands that bullet gets the more that pressure is going to spike.

Your friend can lower the pressure of those rounds by backing the bullet back into the case a few thousandths with a seating die. Or have the chamber reamed to a Wylde, which would also push the lands out further.

Erinyes said...

A man who knows his shit is an invaluable resource.

wirecutter said...

He's shooting new factory ammo and doesn't load, AM.