Sorry if this is a repeat of a question others have asked, I didn't see it covered though. I have a Colt AR-15 Gov't Carbine with a 16 inch barrel, A2 carry handle. I bought it in the mid 90's brand-new. I have 2 questions:
1) Would that be considered a large hole reciever. How can I tell visually the holes look close to the same size.
2) If it is what options do I have for getting a Flat-top upper for it.

Sorry for the super basic questions.

We are discussing 6520 features here:

www.ar15.com/forums/topic.html?b=3&f=118&t=270259

Jump in with your serial number and we should be able to give you specifics.

Quoted: Sorry if this is a repeat of a question others have asked, I didn't see it covered though. I have a Colt AR-15 Gov't Carbine with a 16 inch barrel, A2 carry handle. I bought it in the mid 90's brand-new. I have 2 questions: 1) Would that be considered a large hole reciever. How can I tell visually the holes look close to the same size. 2) If it is what options do I have for getting a Flat-top upper for it. Sorry for the super basic questions.

If your pivot pin is the same size as the rear takedown pin then it's a small 0.250" dia pivot pin.

The large pivot pins are 0.312" dia.

Either size of pins you could get a flat-top upper receiver for it, there are a lot of brands that sells the small pivot size uppers and for the large pivot size Daniel Defense makes it.

The slight problem in switching your upper to a flat-top is that it is higher by about 0.032" which makes your rear iron sight that much higher.

You either have to get a taller front sight post to compensate for this or change the whole front sight base with a taller 'F' type sight.

Changing to a new front sight base is not an easy job to do because the hole pattern in your old sight and barrel have to be exactly duplicated in a new blank (no mounting holes) front sight base.

An alternate easier way is to use a two piece or set screw mounted sight or a railed gas block.