Uppers for M16 Lower

B

Beretta686

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

Jim
 
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