Thad - Wait... I misread your post. I thought you had been given "small pistol primers" and wanted to use them for your magnum reloads. Now I understand that you received "small pistol magnum primers". No you shouldn't use them without backing down your powder to the starting (minimum) load and work up from there. But, a much much better idea would be to go back to the shop and get the correct primer, a 9mm case is too small to be experimenting with. If you haven't used any of the SPM primers the dealer might exchange them. However, some dealers refuse to take back primers or powder for obvious safety reasons. Keep them for the 357 magnum loads you will undoubtedly be making in the near future.
