A Little Lube Does The Trick
Case fire-forming is often plagued with problems when this need not be. Though there are no hard, fast rules; some established techniques do apply.
As a cartridge is fired, pressure is exerted in all directions over the entire inner case wall surface and the base of the bullet.
A common problem is incomplete forming in the area of the case shoulder. One cause of this may be using too light a powder charge. As a rule of thumb, the charge used in the parent case does well as a fire-forming load while leaving bullet weight unchanged. Even then, some cases remain poorly formed.
A technique which I have discovered is to lightly lube the upper body and shoulder area of the case with spray-on sizing lube. Avoid getting lube on the remainder of the cartrige or the lower half of the chamber. As cases are formed, I clean and dry the chamber at frequent intervals with laquer thinner. My case loss is cut to nearly zero using this technique.
