To be sure of forming brass with correct headspace, you could either simply size the brass in your 9X57 dies and load the bullets far enough out to engage the lands, or go one step farther in the loading process and neck the cases up to .40 caliber, then neck one down with the 9X57 dies by leaving the full length die about .025" above the shell holder and gradually screwing it in, attempting to close the bolt on the sized case after each adjustment, until the case is a crush fit in the chamber. Then, leaving the full length sizing die locked in at that position, size the rest of your cases.

Either method will insure that the case head is held firmly against the bolt face and is not moved forward by the firing pin fall.