Apoligies for the thread drift, but you can use those small pistol magnum
primers in any load that calls for small pistol. You will gain MAYBE 25 fps,
10-12 is more typical. Back off your load a couple of tenths to start and
you will be fine. In my minor 40 cal loads, I saw a reduction from 40fps
to 15 fps in the extreme spread when I switched to magnum primers--
they seem to give better ignition with small powder charges.