Numrich guns don't have any kind of flat spot milled into the barrel before the pin hole is drilled. So obviously there are ways of drilling the pin hole without buying a milling machine.
Hungry Horse
the term, "end mill" does not refer to a milling machine, it refers to a specific type of milling tool that is used in a milling machine. these tools have simple round shanks that can be chucked in any drill press chuck as well as any milling machine. a typical 1/4 in diameter end mill, costs about 15 bucks and if used diligently it will last forever. I have a few that are well over 20 years old and still cut fine,.....and I don't have a milling machine. you don't need a milling machine to cut a small flat on a barrel a decent drill press (which most builders have),... will do fine.
the drill guide that Numrich uses probably would cost more than a good drill press,....so us peons use an end mill to establish a plane that is perpendicular o the center line of the hole we intend to drill. Numrich Arms is a company that sells hundreds if not thousands of barrels a year, the cost of the drill guide is then minor in comparison to the proceeds gained by having it.
any time you drill a hole into a slanted surface, you have to have some way of supporting the entrance point of the drill bit, or it will drift,....the smaller the bit the worse the drifting. it cannot be avoided by just a good heavy center punch either, because one side of the drill bit is making contact with the drilled surface before the other side as the bit starts, forces the bit away from the higher side. even a heavy center punch itself will drift because the point is unevenly in contact all the way around the punch and punching at a right angle to the barrels surface to make a small divot for the drill bit to sit in means guessing where the drill bit will finally break the surface and start drilling the hole. these are the inaccuracies I talk about in my post above. the point of the drill bit has to be supported right at the drilled surface, or introduced to a surface that is perpendicular to the center line of the drilled hole,....or the bit will drift as it starts it's cut,... it is simple machine tool geometry. this support comes in the form of an octagonal sleeve that fits over the barrel, is clamped in place and holds a hardened bushing right down tight to the surface being drilled so the bit doesn't have a chance to drift as it starts the hole on a slanted surface. it wouldn't surprise me if they have a dedicated drill press set up permanently with this fixture in place, with several sleeves for the different barrel sizes they sell.
