colt ar barrel

[mad01]

just noticed that on my barrel is stamped: "c mp 5.56 nato 1/7" does this mean I can fire 223 and or 5.56 rounds?

[IraIII]

Yes 5.56 chambers and fires both 5.56 and .223 ammunition. .223 only safely fires .223, supposedly can have pressure increase if fired with 5.56 due to differing lead in the barrel.

[Retired W4]

I agree with Iralll. Beyond 5.56/.223, something for consideration is the twist rate of your barrel. The 1/7 twist rate was utilized for heavier bullets than the M193 (55 grain). The M855 (62 grain) needed the faster twist rate to stabilize the heavier bullet down range. So with your 1/7 barrel you should be using 62 grain bullets, or heavier. The 1/9 barrels are a nice compromise for using either 55 or 62 grain bullets. Of course the old SP1's with their 1/12 rate puts you in a 55 grain box. I'm not complaining, mind you, because I love my SP1 and M193's are cheap and easy to come by, as well as all the commercial 55 grain .223 ammo that's out there.

Just a little food for thought.