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Barrel alignment for retapping base holes/threads

Jason280

Aluminum
Joined
May 21, 2007
Location
Ga
I have a few T/C Contender barrels that I would like to retap from 6-40 to 8-40. I've already picked up the correct size end mill to drill the holes, and have both bottom & plug taps for threading. What I am not sure about, though, is how I ensure that the holes I am milling are straight/perpendicular to the bore. These barrels do have a lug welded to the bottom portion, which hinges into the receiver for lockup, but I am not sure if I can indicate off it to be sure everything is correct. There isn't any taper over the lug area where the factory drilled base holes are located, so it should make it easier.

Am I overthinking using an end mill to recut the holes, and would I be better off simply redrilling them with the proper twist bit?

Suggestions?
 
insert pins in the existing holes and locate each hole. And yes you are overthinking using an end mill, a standard 135 drill is fine.
 








 
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