Does anyone know of a book (or article) that has info on the fire control & pivot pin sizes of Colt receivers? I could have sworn the book "AR15 Owner's Guide" by Duff had photos but it does not. There is only a little blurb about fire control pin sizes and nothing about pivot pins that I can find. I am planning to buy a CMMG M4 upper for my Colt Gov't Carbine so the pivot pin is the only thing I am concerned about.

Also, are all Colt take-down pin sizes consistent, or did they F with that too?

Call/contact Colt Mfg'ring
http://www.colt.com/

Colt "large" pivot pin = .312 dia

USGI "Mil-spec" pivot pin = .250 dia

Your Gov't Carbine lower may have either size depending on when it was manufactured.

There are also offset conversion pivot screws available to mate a USGI size upper receiver with a Colt large pivot pin lower receiver.

I bought my Colt carbine NIB in June of '95. It's a pre-ban (now no-ban) but I am unsure when it was manufactured. Just going by looks, the pivot pin on the carbine is smaller than the one on my 1990 manufactured HBAR. The HBAR I have must have been built using the last of the old style receivers, i.e. no "fence" around the mag catch. Anyway, thanks for the info. I will measure the pin when I get home.