Will a Colt upper fit on Bushmaster lower?

[C-grunt]

I heard that Colt uses different size pins to hold the uppers on. Is this true?

Im hoping this isnt the dumbest question of the year and Im at least a little bit right.

 

[Z71]

I'm a newby to the AR style rifles, well sort of. I had trained and used M16A1 rifles in the National Guard. Had also briefly owned a Colt AR-15 Sporter. However I've been out of the AR field for decades until a couple weeks back.

I had done a bit of research, and it would seem that Colt had changed the pin size on the internals and also the receiver pin size too. From what I learned, it was a political move on Colts part to prevent genuine Colt parts from being interchangable with the huge variety of aftermarket/other manufacturer AR rifles and parts.

As near as I know, this applies mostly to Colts civilian production rifles. The military production being made to the standard AR pattern.

I've heard too, that adaptor pins or bushings are made to make the upper and lowers compatable, but not for sure on that point?

The Century C15 Sporter I bought has a Colt upper(at least most of the upper is Colt made). Supposidly Century put these together from surplus M16A2 rifles. The receiver pins on these are the same as anybody elses AR.

 

[Chipperman]

Will a Colt upper fit on Bushmaster lower?

Some will, and some will not. Some Colt uppers have a large front pin hole that needs an adapter to fit a mil-spec lower.

The good news is that you Can make it fit, it just may not without the adaptor.

 

[MIL-DOT]

Can't answer for the Bushy,but I put an old Colt Vietnam era tri-guard upper on a Rock River lower,it works very well. I'd be surprised if there was any difference with a Bushy

 

[rcmodel]

Colt has went through a lot of different pin sizes & configurations through the years on the civilian AR-15. Supposedly to prevent M-16 full-auto uppers and trigger parts from fitting on a semi-auto lower.

The early ones were stock GI, then after that, the SP1's didn't even have a front pin.

It was a large double ended .312" screw. And not only was it larger, but the upper/lower hole spacing was different then standard M-16.
Thus, the off-set pin/bolt came about.
http://www.del-ton.com/AR_15_Lower_Parts_Adapters_Pins_s/86.htm

Then there were .170" trigger pins for newer colts.

And .154" trigger pins for older colts, every one else's ARs, and the military rifles.

I hear they are now back to standard pins again, but I could be wrong, as I haven't bought a new Colt lately.

rcmodel

 

[Zach S]

A lot (okay, most) of the civi Colts had the larger screws up front, but if its a surplus upper (and I think LE uppers as well), it will be milspec, and will work on any milspec lower (basicly, anything other other than a civi colt that uses the screws).

The funny thing about the offset pin in the link above is that it says its to use large hole uppers with mil-spec lowers, however in the pic its for mil-spec uppers on large hole lowers. If you order it, you might wanna call first.

M60Joe might be able to install a bushing in a large hole upper so it will mate to a milspec lower using a standard pivot pin. There are pics on his site of bushings installed in lowers, but I dont recall seeing any of uppers.

 

[bturnn]

Hey There,
I just finished placing my early 80's Colt SP! Sporter upper half on my S&W M&P 15 lower receiver. The Colt has the "Big Pin" and the Smith lower is new Milspec. You will need to order the Bushing adapter and not the offset pin. Only cost a few dollars from Midway.
Good Luck!
Bruce