Basic ?'s about AR's

[jukk0u]

greetings,

May I please solicite your indulgence to ask a few basic (dumb) questions?

I have an AR "Sporter" H-bar 20" from COLT. Purchased in 1994.
Just behind the front sight the barrel is stamped: C MP .556 NATO 1/7 HBAR.

The side of the lower receiver is stamped (cast?) :
Sporter
Match HBAR
cal .223
Colt mfg co Inc
hartford conn

No model number is ascertainable. (6601?)

With the rifle I recieved a small 4"x 4" booklet that was intended for three different models. It lists the appropriate ammo as:
223 Remington (Rem.) (5.56mm)

My questions are...:
Is this rifle safe for 5.56 ammo? (like 77gr. mk262?)I have only cycled .223 through it.

Which part of the rifle determines the ammunition? I should like to know if I can swap out the upper for a flat top capable of handling 5.56. (Yeah I know Colt is particular ... I used to own Fords... I'm kinda that way too. I am hoping a Larue upper will be applicable but I haven't looked into it, or maybe just the stripped a3 upper...)

I haven't yet measured the pin size..
Thanks for humouring me, folks

 

[Redmanss]

Re: Basic ?'s about AR's

You have a 5.56 chambered barrel as indicated by the stamp by the FSP. The stamp on the lower receiver is irrelevant. Run either/or as you please.

If you still have any doubt, consult a gunsmith with the appropriate gauges to confirm the markings on the barrel.

 

[jukk0u]

Re: Basic ?'s about AR's

Many thanks, sir, for both the information and your service to our country.