I would like to know how do you guys countersink the plunger tube hole on your 1911 receiver and also the grip bushing hole? Jerry Kuhnhausen has been recommending a "countersink cutter" (pp.80 of The US m1911/1911a1 pistols vol.II) But I dont know what size and where to get it.
I've had pretty good luck with a ball end cutter in a Dremel tool. It is easy enough to get it down into the magwell to cut a relief on the edge of the plunger tube holes.
I also use a ball end cutter in a dremel but will not use a stone to do this as it too easily grabs metal and skips off of its own accord because it has too much bite. I have found using a diamond ball end cutter works much better because it is removing so little material that it will not bite too much and skip off bouncing around the inside of the magwell.
This is who I use for my diamond coated bits: widgetsupply.com
Or you can purchase one of KT's 1911, they come with the plunger tube already countersunk.
I already did order one from you several weeks ago. It is the one that has an extended dust cover.