Basic AR Question

[HighLifer]

Guys-

I'm about to purchase a pre-ban Colt 20" AR in very good condition. The upper is an HBAR A2

My question is - if in the future I decide that I'd like a Carbine Flattop - will another manufacturer's upper fit the Colt lower? With most manufacturers I know they would, but is the colt front screw a larger diameter than the typical front pin used by Bushmaster, RRA, etc. etc.? I'm sure a new Colt flattop would cost a lot more than the same product from one of the other brands

Appreciate any insight, thanks!

 

[abomb60]

Any small pin upper will fit on a large pin colt lower with the use of an offset pin although the colt lower may not have a large front pin so you'll have to check. If you build a new upper Daniel Defense makes an upper receiver that has the large colt pin and is an A4 style flat top.

<---- I used one when I built the SBR upper in my avatar picture.

 

[thepossiblehuman]

Yup. The small pin adapter works great. Funny. I'm about to sell my 20" HBAR pre-ban Colt Sporter along with my Colt Diemaco 14.5" upper (pinned YHM Phantom Flash hider to meet NFA 16" barrel requirements - and full auto capable bcg). Guess I'm not the only one in serious need of $$$$! I used the adapter and it fit perfect. I just wish I got to fire it before unloading. Oh well. So it goes...

 

[LKB3rd]

I have a Colt upper that is the standard small pin, and it swaps onto my Olympic lower fine. As already pointed out, even if it is the large pin, you can get pins to make it work.

 

[vellnueve]

It can be made to fit using several adapters.