Mixing and matching AR lowers and uppers

[Justin]

If you stick an upper from one company onto the lower of another company, how likely is the thing to work with only the usual level of hassle?

Said another way, can you stick an Armalite upper on a Bushmaster lower? Or a DPMS upper on a Rock River lower, or any other combination?

Do people actually do this, and is it a big hassle?

 

[Hkmp5sd]

No problem mixing. I have a Colt M16A1 lower with a Bushmaster 14.5" upper and it worked perfectly the first time I put them together.

If you are swapping bolt carriers into different uppers, you may need to check the headspace.

 

[Atticus]

It's no hassle at all. If they are mil spec there should be no difference. Exceptions include some early receivers made by Colt and Armalite. Explanation below. No biggie though-pins exist to make the two work together.

http://www.biggerhammer.net/ar15/uppers/

Small Hole vs. Big Hole

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.

 

[Badger Arms]

No problems at all mixing and matching. I don't buy Colts for political reasons. I'd have bought them years ago before they sold out and I'd buy them again with standard holes and parts and without the receiver block.

 

[dleong]

If the uppers and lowers are mil-spec, you should have problems mixing and matching. My three ARs have the following upper/lower combinations:

1. DPMS/Eagle Arms
2. Rock River Arms/Eagle Arms
3. Rock River Arms/DPMS

Absolutely no problems with fit in these three combinations, though the colours don't quite match up.

DL

 

[mark mcj]

Most of the time there is no problem.
From what I've seen, some times a shooter might have to remove a small amount of metal from the rear pin lug of the upper to get the upper all the way down in the lower.
I've seen this three tomes when matching a RRA upper with a Bushy lower. And once when using a RRA lower and a Bushy upper.

 

[Redlg155]

Over at AR15.com there is a bit of discussion about mating a Bushy upper to a RR lower and slight fit problems.

I've mated at least 3 RR uppers and 1 Armalite upper to Bushy lowers with zero problems. Also a couple of JT kits to a Bushy and Oly lower with no problems.

Based on what I've seen Rock River lowers also seem pretty tight the first time you stick the upper and lower together. A little oil and working the halves together a few times usually breaks things in nicely.

Good SHooting
REd