Boomer68, Why not try a few Cream of Wheat blanks first? I use about 20 grs. of DuPont 700, shotgun powder under the cereal. Overworking your brass is still a worry, though. I was reforming some 8mm Mags to my similar 416 Wildcat, and lost about half. But these were junk cases which had already been formed down and fire formed in the 8mm Mag chamber, from R-P 375 H&H virgin parent brass. This was a last resort to get some 8mm Mag sample cases for my reloading die, and forming die, CNC'er. I had necked them down in steps, as these Hornady 375 Ruger Basics were too tough to work down, any other way. The R-P 375 H&H virgin brass was much easier to work over. But half of about half a dozen, said "later", in doing this for a You Tube video.
Your case mouths will probably remain somewhat belled over, but you can deal with those, with your .456 inch expander button. This Cream of Wheat drill doesn't eliminate the need for neck annealing. After two or three firings, my 44 x 356BB cases, start to grow minute cracks right at their case mouths. So far, I've avoided annealing by merely trimming back these same case mouths.
