Okay.. I have been using my YHM gas block flip up front sight for some time now.

At first I just tightened the set screws and went shooting...eventually they worked out.

The I used lock-tight..this has held so far..

What I was wondering is if one were to take a drill bit a size smaller than the set screw.. and drill into the barrel making a place for the set screw to seat in would this work even better than lock-tight?

What are your opinions?

NO.

Just make sure that the treads are free of oil before you apply Loctite, and you won't have to worry about it.

I would countersink the barrel at the setscrews.  That sight is not that secure with just those setscrews and one simple drop or bump could easily move your FSB and throw your whole zero off, or even shut off your gas system should it move far enough.

The countersink is no guarantee, but it will definitely help.  And yes, apply Loctite to clean, degreased threads, otherwise it may not set up correctly.

Finally, countersink the barrel AFTER you have zero'd the sights.  If done before and you have a cant in your FSB, you would have to live with it that way.  I would set up the FSB so that the windage is exactly centered in your windage adjust, then setscrew the FSB in that spot.

Good luck.