Originally Posted by MikeS
Has anyone ever tried to convert a small pin upper by drilling out the hole to the large pin diameter? I know the holes are are offset but have a fiend who is a machinist and it seems like the trick would be to devise a holding fixture to line everything up.

I picked up a small pin Colt flattop upper to put on my large pin Colt service rifle lower and am tired of messing with the offset pin adapter.
Mine's just the opposite, i.e., a Colt lower and a Bushmaster upper. I just use the pin adapter to join them.

[Linked Image]