To the OP,mcould you take the spud,drill and tap for the correct thread and use it that way?
I myself like the M die. Some folks love them some cuss them. I have not as of yet had an issues that I can point a finger at the M die caused.
It should open the brass back up to a more standard size and length for a cast bullet. But, what is standard when size is king?
Got into an interesting sit down over coffee discussion on this some time back with a couple of guys.
Sizer die may size down to much. Then the M die is not quite enough, but better. Then on some type crimping dies it may actually swag down our perfectly sized bullet in the case
A bushing die of proper size may be in order in some instances.
I was loaned a lee universal belling die,mi returned it in short order. My K31, Krag and 1903 had no tolerance for its use. The 03 being the pickiest of the three leaded in about 10 rounds.
I pulled them when I got home and the case had sized the bullet down sure enough. I suspected it when I seated them.
I have since got a set of dies that sizes on the large end of things, but I still use the M die.
I do have to be careful with the K31 with its tight dimensions.
Jeff