Colt 9mm lower to different brand 5.56 or other cal upper

[futureAT]

Hi guys. I inherited a few firearms after my dad passed away and I've been learning all I can about them and I've become very fond of shooting and working on them. One of the rifles he had is a Colt 9mm carbine, semi-auto, 2 position telescopic stock. It's a real joy to shoot and I do not plan on selling it but I would like to have a bigger caliber AR (5.56 or bigger) but I don't exactly have the money to buy an entirely new rifle and I'm not sure if it would be possible to purchase a 5.56 upper from a different manufacturer (such as RRA or whatever) and put it on the Colt 9mm lower I have. I've read some other posts and saw that people say it would need a diff hammer and possibly a new buffer. . I know i'd obviously have to take out the existing mag block but what else would I need to do for it to function properly? Can I use a RRA upper on a Colt lower? or would it have to be Colt upper? What all would I have to change in the lower (besides mag block) for me to swap out the 9mm upper for a 5.56 upper? Thanks for any help or advice! btw the pic with the 2 AR's is in my local pawn shop. the top is my 9mm colt, the bottom is some really strange brand but it is in 5.56. we opened them both up to compare the internals and they look like they would mate up just fine. What do you think?

[khc3]

It's possible that the pivot pin in your Colt lower is oversized compared to the standard AR specs. If so, Colt makes an offset adapter pin to use with uppers with standard pivot pin holes.

Aside from that, as you said, you'd need to remove the mag block, probably need a regular AR hammer. You should be able to use your 9mm buffer. It may not lock back on empty mags, or it may cause functioning problems with weak ammo, but I would try it first before buying a CAR or H buffer. They're pretty cheap though.

With that you should be good to go with any upper you want.

[futureAT]

Yeah thats what the guy at my local pawn shop said too. Oh and btw the front pivot is a two sided screw design. I haven't measured it so I couldn't say how thick it is but I did find some retailers that have the adapter pivot pin. Well thanks for the reply brother. That's helpful!