AR-15 Upper and Lower compatibility

Mausermolt · January 10, 2013, 10:49 AM

Are most uppers and lowers pretty much interchangeable? i bought a Rock River Coyote Carbine Upper, i dont have a lower yet because im out of the country and the prices are way to ridiculously high right now. but i have a Bushy back home thats a full size XM-15E2S 20'' model. could i just swap out the uppers?

slugcatcher · January 10, 2013, 11:02 AM

Most of them are. Your combo shouldn't be a problem. The Colt Spoters from the 90's used a non-standard take down pin but you can buy adapaters to use those with standard uppers or lowers.

Mausermolt · January 10, 2013, 01:18 PM

ok MOST of them are. tell me which ones wont be compatible with the RRA please

CTS · January 10, 2013, 09:16 PM

A mid 90's Colt with the large pins. Just as was previously stated. All others are interchangeable.

Theohazard · January 11, 2013, 01:59 AM

The only compatability issues you'll have will be aesthetic: the finish on your upper might not match the finish on your lower. Otherwise they will work just fine.

Mausermolt · January 11, 2013, 07:30 AM

great! thanks

Mobuck · January 11, 2013, 08:00 AM

You may find an occasional combination that's too tight or is looser than you like. For the loose fit, there are little rubber thingies that tension the rear pin making the fit feel tighter. For that occasional "too tight" fit, fortunately it seldom happens. I've seen some filing done on the upper but I don't condone this solution.
I was doing some mix-n-match a couple of weeks ago trying to find exactly what my older Son was looking for in a hunting carbine. When he'd picked the lower with the trigger feel he liked and the upper with the features he wanted, guess what, the fit was tighter than I felt comfortable with. A simple 5 minute job to swap fire control parts to another lower but had there been only one lower available, that would have been unhandy.

January 10, 2013, 10:49 AM	#1
Mausermolt Senior Member Join Date: June 16, 2007 Location: Ory-gun Posts: 508	AR-15 Upper and Lower compatibility Are most uppers and lowers pretty much interchangeable? i bought a Rock River Coyote Carbine Upper, i dont have a lower yet because im out of the country and the prices are way to ridiculously high right now. but i have a Bushy back home thats a full size XM-15E2S 20'' model. could i just swap out the uppers? __________________ Molon Labe

January 10, 2013, 01:18 PM	#3
Mausermolt Senior Member Join Date: June 16, 2007 Location: Ory-gun Posts: 508	ok MOST of them are. tell me which ones wont be compatible with the RRA please __________________ Molon Labe

January 11, 2013, 01:59 AM	#5
Theohazard Senior Member Join Date: April 19, 2012 Location: Western PA Posts: 3,829	The only compatability issues you'll have will be aesthetic: the finish on your upper might not match the finish on your lower. Otherwise they will work just fine. __________________ 0331: "Accuracy by volume."

January 11, 2013, 07:30 AM	#6
Mausermolt Senior Member Join Date: June 16, 2007 Location: Ory-gun Posts: 508	great! thanks __________________ Molon Labe

January 10, 2013, 11:02 AM	#2
slugcatcher Junior Member Join Date: April 27, 2010 Location: Texas Posts: 14	Most of them are. Your combo shouldn't be a problem. The Colt Spoters from the 90's used a non-standard take down pin but you can buy adapaters to use those with standard uppers or lowers.

January 10, 2013, 09:16 PM	#4
CTS Senior Member Join Date: November 6, 2011 Location: NE Georgia Posts: 1,070	A mid 90's Colt with the large pins. Just as was previously stated. All others are interchangeable.

January 11, 2013, 08:00 AM	#7
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	You may find an occasional combination that's too tight or is looser than you like. For the loose fit, there are little rubber thingies that tension the rear pin making the fit feel tighter. For that occasional "too tight" fit, fortunately it seldom happens. I've seen some filing done on the upper but I don't condone this solution. I was doing some mix-n-match a couple of weeks ago trying to find exactly what my older Son was looking for in a hunting carbine. When he'd picked the lower with the trigger feel he liked and the upper with the features he wanted, guess what, the fit was tighter than I felt comfortable with. A simple 5 minute job to swap fire control parts to another lower but had there been only one lower available, that would have been unhandy.