Tried seating small pistol primers using RCBS universal priming tool, which I never really like using for small primers as it seems to work better with large primers. Used a Redding #1 shell holder for which .357 Magnum seems to fit snugly. I had thought this was appropriate for .357 Magnum and I do use it for .41 Colt. I now see the #12 shell holder is for .357 Magnum, but there is no wiggle room at all. I visualize each primer to ensure not crooked and placed in the right direction. Nonetheless, at least 50% crushed, improperly seated. I would think it IS the wrong sized shell holder, in hindsight, except it seems the fit is so snug that the #1and #12 shell holders seem virtually the same. Advice? I mostly load large primer rounds—and now I see why!