Any idea what the threading is on these. Seems the one or two calibers I'd like are out-of-stock every place I've looked. One would think that a piece of 1x fired or new brass could be drilled and threaded in lieu of purchasing the same.

I shoot an A.I. caliber that they don't even list. Call them up and they'll tell you how to send in 2 fired cases and get them made for you. Think about it that's better than off the shelf because it's fire formed in your chamber. Costs around $15.00.

5/16"x36tpi I make all mine on a lathe.
you can make a guage by using a once fired case in the chamber you want to measure.
I would expand the neck and cut two slots in it for a very light bullet grip
Dave

Drill primer pocket with a letter "I" drill bit. I would drill a smaller diameter pilot hole first.
Put case in padded vice jaws for the drilling and tapping. Better, as hivelocity recommends, is a lathe.
I never felt the need for any grip on the bullet.
But that's just my way.

muck