I didn't do the experiments.... It has been said that the WSPM primers are the same cup as the WSPP...That being said, if the SPP will seal the cup, then the SPMP will seal as well. There was a thread on primers on here not long ago, and somoeone actually corresponded with several of the primer manufacturers and got the cup hardness of quite a few of the different types. The only difference (IIRC) between the WSPP and the WSPMP was the heat of the flame... For those that want the linki