Uppers for M16 Lower

Beretta686 · February 23, 2014, 01:23 PM

I'm expecting my Colt factory M16 to transfer to me here in the next few weeks, but I'm a bit confused as to what uppers to run on it.

I have several uppers for my SBR AR-15 that have AR-15 bolt assemblies in them. Will I need to switch those out to run full-auto with my M16? Also if I have an M16 bolt in my upper and run it with my SBR, will that get me in trouble?

James K · February 23, 2014, 01:45 PM

It isn't the bolt, it is the bolt carrier that is different between the semi-auto and full auto versions. The FA bolt carrier is made to trip the auto sear; the SA carrier is cut away so it can't operate either a regular auto sear or a DIAS.

If you are buying a selective fire rifle, then it should have the correct upper and the appropriate bolt carrier in it, so I am not sure what your concern is about another upper.

Jim

Beretta686 · February 24, 2014, 06:40 AM

My concern isn't the upper. It's if I'll need to replace the bolts carriers in the uppers I already have to run full-auto with my M16. And if so, will have M16 bolt carriers in an AR15 cause me legal issues.

Willie Lowman · February 24, 2014, 09:58 AM

FA bolt carriers won't cause legal issues unless your state has some screwy law prohibiting them. There are many manufacturers that sell their semi auto rifles with FA bolt carriers in them as factory parts.

A more realistic concern would be if your M16 will run properly with short barrels. Sometimes a buffer swap is needed. Sometimes the sear timing needs adjusted, but that would be more a problem from worn parts.

Skans · February 24, 2014, 02:09 PM

From what I can remember, the Colt M16 lower should directly fit onto most upper receivers, so long as they have the cut in them for the auto-sear. The older Colt AR (semi-auto) upper receivers didn't have the auto-sear cut, but I believe all of the A2 uppers and M4 uppers have the cut. The semi-auto Colt AR's had a different size pin/bolt hole to make it a little more difficult to directly bolt on an A2 upper. So, to put an A2 upper or other "full-auto" capable upper required an offset bolt. However, the M16 lower obviously doesn't have this problem.

So basically, unless your older uppers are from an older Colt AR (no relief cut for the auto-sear), you shouldn't have any problem.

James K · February 24, 2014, 02:59 PM

Since your lower is a registered machine gun, anything else is just parts. You can use any upper or parts thereof you want.

Jim

February 23, 2014, 01:23 PM	#1
Beretta686 Senior Member Join Date: May 11, 2005 Location: Texas Posts: 761	Uppers for M16 Lower I'm expecting my Colt factory M16 to transfer to me here in the next few weeks, but I'm a bit confused as to what uppers to run on it. I have several uppers for my SBR AR-15 that have AR-15 bolt assemblies in them. Will I need to switch those out to run full-auto with my M16? Also if I have an M16 bolt in my upper and run it with my SBR, will that get me in trouble? __________________ "Our contract called for 16 cases of rifles and ammunition for $10,000 dollars, not a machine gun...........That is our present to the General"-Pike Bishop “When fascism comes to America, it will be wrapped in the flag and carrying a cross.”

February 24, 2014, 06:40 AM	#3
Beretta686 Senior Member Join Date: May 11, 2005 Location: Texas Posts: 761	My concern isn't the upper. It's if I'll need to replace the bolts carriers in the uppers I already have to run full-auto with my M16. And if so, will have M16 bolt carriers in an AR15 cause me legal issues. __________________ "Our contract called for 16 cases of rifles and ammunition for $10,000 dollars, not a machine gun...........That is our present to the General"-Pike Bishop “When fascism comes to America, it will be wrapped in the flag and carrying a cross.”

February 24, 2014, 09:58 AM	#4
Willie Lowman Senior Member Join Date: March 5, 2009 Location: Uh-Hi-O Posts: 3,006	FA bolt carriers won't cause legal issues unless your state has some screwy law prohibiting them. There are many manufacturers that sell their semi auto rifles with FA bolt carriers in them as factory parts. A more realistic concern would be if your M16 will run properly with short barrels. Sometimes a buffer swap is needed. Sometimes the sear timing needs adjusted, but that would be more a problem from worn parts. __________________ "9mm has a very long history of being a pointy little bullet moving quickly" --Sevens

February 23, 2014, 01:45 PM	#2
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	It isn't the bolt, it is the bolt carrier that is different between the semi-auto and full auto versions. The FA bolt carrier is made to trip the auto sear; the SA carrier is cut away so it can't operate either a regular auto sear or a DIAS. If you are buying a selective fire rifle, then it should have the correct upper and the appropriate bolt carrier in it, so I am not sure what your concern is about another upper. Jim

February 24, 2014, 02:09 PM	#5
Skans Senior Member Join Date: November 20, 2008 Posts: 11,132	From what I can remember, the Colt M16 lower should directly fit onto most upper receivers, so long as they have the cut in them for the auto-sear. The older Colt AR (semi-auto) upper receivers didn't have the auto-sear cut, but I believe all of the A2 uppers and M4 uppers have the cut. The semi-auto Colt AR's had a different size pin/bolt hole to make it a little more difficult to directly bolt on an A2 upper. So, to put an A2 upper or other "full-auto" capable upper required an offset bolt. However, the M16 lower obviously doesn't have this problem. So basically, unless your older uppers are from an older Colt AR (no relief cut for the auto-sear), you shouldn't have any problem.

February 24, 2014, 02:59 PM	#6
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	Since your lower is a registered machine gun, anything else is just parts. You can use any upper or parts thereof you want. Jim