AR15 Small hole to Large hole?

[y2k]

can a guy just enlarge ie drill out the small hole upper so it fits on large hole lower? Instead of those conversion screw sets from brownells?

 

[Lee Enfield]

generally no.

The front pivot on the lower is larger than an A1, it's actually larger than an A2, consequently there isn't very much meat to drill out on a push-pin upper.

Daniel Defence makes a flat-top, "large hole" upper. Wolverine Supplies catalogues it.

 

[MasterMC]

I would try inserting the bushings (press fit) and use small pins on the large hole lower receiver. It might work better and no drill required. Just my 2 cents.

 

[tiriaq]

I believe it is not just a matter of hole size, but also hole location. The adapter systems - screw, bushing - are offset slightly.

 

[Rugerman]

I believe it is not just a matter of hole size, but also hole location. The adapter systems - screw, bushing - are offset slightly.

That is correct. Just get one from Rick at ATRS. You don't want to mess that up! Not expensive and an easy fix.

 

[browningautorifle]

I tried drilling one and it doesn't work that well. Use the conversion kit or buy a push pin lower to match.

 

[Leg]

Like has been said already, the holes are offset, so enlarging the existing hole won't work.

Daniel Defense sells large hole flat top uppers, that would be your easiest solution. Another alternative that I've seen pictures of is to fill the holes on the lower with aluminum rod, pinned to ensure they don't move, and then drill the small hole in the proper location. You'd still need the two part screw (they make a small version) because the lower won't be able to retain the pivot pin.