Hey guys,

Before you ask, yes I did a search but Im still confused.

I have a Colt marked Match Rifle, lightweight postban rifle I bought before the M4 craze. I would like to keep it all Colt, but as everyone knows Colt prices are crazy. Ive read about the different pin size uppers and lowers and I think Im more confused than when I started. I guess my question is, if I purchase an M4 upper (RRA, Bushmaster, etc)there is a way to mount it on my colt lower? I see that Bushmaster has a pin kit and Im assuming that would be all I need.

Next question: Can I use my colt bolt or are the bolts matched to the uppers in some way. I was under the impression that the bolt should be interchangable between rifles. With the plethora of uppers out there I want to make sure my colt bolt won't blow up another manufacture's upper.

Thanks ahead of time for any answers.

If your Colt lower has a large diameter pivot pin hole, you'll need a special pivot pin when using other uppers that has the std(milspec) diameter pin hole, otherwise uppers should be compatible regardless of make.

If your lower is grey, like alot of Colts, color match may become an issue for you.  So I would recommend a closely matched grey receiver, if you want a good color match.

Your Colt bolt will work with all other AR manufacturers and is probably one of the higher quality bolts out there, so I would stick with the Colt bolt, myself.  A headspace check to the new barrel you use wouldn't be a bad idea for insurance.

Thanks for the quick answers.

Any ideas on which uppers match the colt coloring the best? Mine actually looks pretty dark. The rear sight is a grey color but the rest is a dark, dark grey if you would call it grey at all.

If it's dark, almost black, you probably won't have color matching problems.  Some early Colt receivers were finished with a distinctive grey color, however they no longer do it.

Sounds good. Im guess im off to the gunshop to get this thing started. Does the madness ever end?

Quoted: Does the madness ever end?

NO.

Quoted: Sounds good. Im guess im off to the gunshop to get this thing started. Does the madness ever end?

Your MADNESS has just started,Good luck.

If you have a Colt "Match Target" model it will probably be equipped with the small pivot pin. Check to see if your pivot pin has screw slots on the left side only (small dia.) or on both sides (large dia.).

It's a very good idea to get your headspace checked anytime you change the barrel or install a new upper and use your old bolt. A gunsmith can do it for a minimal charge. It's good insurance!

The match target should be more black than grey anyway depending on how old it is.  The earlier pre-ban models are grey.  You should be O.K.  with the front pivot pin size too.  But you know how Colt can be ?

This should also help clear things up, I pulled this from Biggerhammer  If you click on the link there is more info you might need on the site.
Colt owners often refer to having a small or large hole upper receiver (and corresponding lower receiver). Small hole receivers of .250" are the "milspec", but during early production by Colt for the civilian market, they produced rifles utilizing a .315" spec, so as to preclude use of military uppers on civilian lowers. This production lasted until roughly 1993-1994. As a general rule of thumb all Colt "unblocked" lower receivers, are large hole, while pre-ban "blocked" lower receivers represent transition years where occasional variations popped up.