When drilling holes in a barrel(for mounts bases) what is the miniumum safe amount of metal that should stand between the bottom of the hole and the chamber or bore?
If we were to drill a hole into a barrel over a chamber to accept the stud of a Leupold QR ring,which is much larger in dia. than a mounting screw, would the thickness of metal have to increase between the bottom of the hole and chamber area because of that larger dia?

The only simple answer to that question is to drill the holes no deeper than necessary to get sufficient thread engagement for the screw. A good ball park figure for this is that the threaded hole should be as deep as the major thread diameter of the screw to get needed thread engagement.

The formula I was taught for drilling over a chamber is: Barrel diameter minus barrel groove diameter, divided by two, minus .125â€. This will give you the safe maximum depth you can drill into that particular barrel...but don’t even go that deep if you don’t have to to get the thread engagement I mentioned above.

over the chamber there should be plenty of material to allow a full 1.5 diameters of thread....more is not needed.

Over the front sight on a thin barrel I drill in a milling machine to .03 short of the point of the drill breaking thru.

Years ago I experimanted on a 8MM mauser barrel by drilling and tapping the front sight holes all the way thru to the bore. The pressure did not blow the screws out of the barrel as I suspected might happen....it's not good to do this but the key here is not to drill to break thru.