Creating Brass for the B&M's
For all the B&M series the brass is based off of Remington Ultra brass. One takes any RUM brass and cuts and trims it to 2.240 inches. This gives you first of all, 50 B&M. Just run through the size die and load.
All the basic 50 B&M brass then can go to all the B&M cartridges by just running the basic brass into the various B&M size die. It's just that simple. 475 B&M, 458 B&M, 416 B&M, 375 B&M, and 9.3 B&M.
This is an example of creating a 9.3 B&M, which is the smallest diameter the B&Ms come in.
Basic brass to run through the 9.3 B&M Size die.
With any bottle neck cartridge, one wishes to size the new and unfired case to the point of where it just goes into your rifle with slight resistance. This means the shoulder is bumping in the chamber just ever so slightly and keeps the brass from flowing too far forward when it is fired. This keeps your brass from head separation in the future. Once fire formed, then one can full length size the cases to the point that they go in the chamber with ease.
As you see below the fire formed case has slightly sharper edges on the shoulder than what the formed case has.
A few examples of the current test targets
For the Super Short Series the process is identical. The B&M Super Short Series, 50 B&M Super Short, 475 B&M Super Short, and 458 B&M Super Short all use Winchester Short Mag or WSM brass. It too is cut and trimmed, but to 1.640 inches. Then if you have a 50 B&M Super Short, size, load and shoot. The size die for the 475 and 458 B&M Super Short forms the case to their specs, and it is pretty much the same, size, load and shoot as well.
This is the basic WSM brass about to be formed to 475 B&M Super Short.
Cutting the parent brass is the biggest chore of creating a B&M case. In the case of the standard B&Ms, one has to take RUM brass, cut and trim to 2.240 inches, then some possible trimming after it's formed. With the Super Shorts, same story, cut and trim WSM brass to 1.640, and some trimming may be required after forming. One can do this on your own easy enough if you have proper equipment. You can even do this the old fashion way with a hacksaw! I really do not have the time, nor inclination to do all this cutting myself. I normally purchase from Midway 500 or so pieces of either RUM or WSM brass, then I have a friend of mine cut and trim. He charges me $0.75 each to cut and trim, then whatever the brass costs. Brass has gone up since the last I had cut. I had $1.50 each piece invested on what I have currently. The next brass I have cut and trimmed is going to cost a bit more I am afraid. I try to keep this basic brass on hand for all those who rather not cut and trim their own. Just ask.
Case life is extremely long for all the B&M cartridges. I mean extreme too, I have some that have been fired an estimated 75+ times without showing any problems at all.
Hope this helps some, and please, any problems or issues contact me.