I'm currently using the RCBS Cowboy ,mouth exp. die for 30-30Win shortened to work with my cartridges. This does the same as the "M" Die and expands the full length of the neck, while slightly belling the case mouth. I AM looking for BR accuracy and I'm NOT going to crimp. The COL that I'm working in, would require the crimp to be in a non-cannelure portion of the bullet, which would cause deformation. Crimping also requires the soft lead bullet to "uncrimp" the case as it passes through the reduced opening. The projectile becomes slightly deformed as a result. I have tried crimping and saw my groups open immediately with no other changes made. This is fine for a "Thutty-Thutty" or BPCR where 1" plus groups at 100yds are tolerable. (I'll get flames for that last sentence
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What I'm hoping to determine is what size necks I should be creating to obtain and maintain the right amount of "hoop tension" on the bullets. The brass has a certain range of elastic deformation before permanent deformation occurs, and I'm trying to work within that window.
I am going to order a VLD reamer next, and I may make a couple of steel bushings on the lathe just to find out what size works best. The Redding catalogue recommends buying "1 or 2 sizes above and below the target diameter" for neck-sizing bushings. Good for them. They are 20$ each not including shipping.