Quote Originally Posted by rpoL98 View Post
on AR-15's, if not already tapped, I tap the hole for the take-down pin detent & spring for 2-56 set screw. it's a very common mod. Some AR-15 lowers come with that mod.
I think a 2-56 set screw is going to be too small for that hole. Are you sure you're not using a 4-40? I've seen some companies using a 6-32 even. I've been using a 4-40 for 30 years.