I recently picked up a T/C Contender Super 14 barrel in .30-30. These barrels use 4x 6-48 tapped holes in the rear for a scope base, and when this one arrived, two of the holes were bare and two had filler screws in place. This should have been a hint. The first filler screw was a bear to remove, even after soaking with penetrant and liberal amounts of heat. The rearmost filler screw ended up breaking off below the surface, and no method I had available would extract. I was able to get the majority of the screw drilled out, with the only remaining portion being the pieces still wedged in the threads themselves. I tried chasing the threads with a bottoming tap, to no avail. The tap will thread maybe 1-1.5 complete threads, except it binds enough that tap breakage is a concern. I've tried backing out and running forward a couple times, it still binds at roughly the same position.
I think at this point the only solution is to drill/retap to the next larger size, which would be 8-40. I've never drilled/tapped anything this small or this precise, so I am just a little intimidated. My main concern is ensuring everything is lined up correctly, which shouldn't be an issue as I currently have the hole to guide me and the flat portion off the barrel boss/hinge to serve as a flat base to locate in the mill vise.
Any tips or suggestions on how to move forward? Do I even need to use the mill, or could this just as easily be accomplished with a drill press?
I think at this point the only solution is to drill/retap to the next larger size, which would be 8-40. I've never drilled/tapped anything this small or this precise, so I am just a little intimidated. My main concern is ensuring everything is lined up correctly, which shouldn't be an issue as I currently have the hole to guide me and the flat portion off the barrel boss/hinge to serve as a flat base to locate in the mill vise.
Any tips or suggestions on how to move forward? Do I even need to use the mill, or could this just as easily be accomplished with a drill press?