.223/5.56 ?

[mnhornet]

Dumb question from a guy hoping to build or sneak an AR into the house in the near future. If I buy an upper that says 5.56, can I only use military ammo, or can I run commercial .223 through it.

[Survey Punk]

Main diff. between a NATO chamber and .223 is the length of the leade, or distance between the end of the chamber and the origin of the rifling. This is due to the length of the M856 tracer bullet at almost 1".
You'll be just fine firing storebought ammo in a NATO chamber but a 5.56 tracer in a commercial chamber can cause high pressure.

JB

[MAINER]

Gererally OK to shoot .223 in 5.56mm chamber, but not 5.56mm in the .223 chamber.
5.56mm chambers have a longer throat.

More info:
http://www.fulton-armory.com/556-vs-223-Chambers.htm

And:
http://www.winchester.com/lawenforcement/news/newsview.aspx?storyid=11

[mnhornet]

OK, sounds like if I get a 5.56 chamber, I may lose accuracy by shooting .223.
If I go with a .223 chamber, then I should only fire .223 in it to avoid a potential overpressure/KB. I think I got it now.

[Wolf Spyder]

I would buy the 5.56mm chamber.

There is really no (or very little) effect on accuracy when using store bought .223 Rem cartridges. My home built Ar15 / M4-gery (with 5.56mm chromed chamber, barrel, carrier, bolt) is a 2-3 MOA shooter with Nato Surplus and a 1 MOA shooter with Hornady 62 grain A-max or V-max what ever it was...

If you want a tac-driver .223 Rem, then buy a Tactical bolt action rifle with a fat 1 inch diameter 18 inch barrel.

If you want a fun gun in an AR15 platform, then buy an AR15 in 5.56mm.