An 8x40 #28 TiN coated drill bit from Brownells (361-651-028) made quick work of drilling the holes for the mount screws, followed up with an 8-40 bottom tap (748-002-840).
The bottom tap is necessary to bring the threads all the way into the blind holes on the barrel.
A bottom tap features almost no taper at all, and is intended to cut threads almost all the way to the bottom of a blind hole.
If you want threads almost all the way to the bottom, a bottom tap would be used after a plug tap cut as many threads as it could.
Go to "Search and apps" tab, then at the bottom tap
Defaults, then choose a new app for e-mail, music player, Web browsing, photos, video player and calendar.
In some cases, you have to begin by using a starting tap with a high lead on it, followed by a bottom tap
, if it is a blind hole.
For good squat form, try standing about six inches in front of a chair or bench, and lower your hips until your bottom taps