sp magnum primer substitute for sp pistol primer

Was goimg thru the storage container and realized im down to only 300 sp primers. Last year had a guy give me a bunch of stuff to reload 357mag, which included about 2k worth of sp magnum primers. My boy moved to Austin and took his 357 with him, so i wont b reloading this round for a long while. So my question is, can i sub in the magnum primer in place of the std sp primer. This will be for 9mm and 45gap middle of the road plinking loads. Using w231 for 9mm. Tightgroup for the gap. Google search was all over the place, some said yes some said no. Some said pressure increase, some said no issues? Ill back the loads down about 5% if able to substitute. Thanks in advance for any input.

Yes, just drop the powder charge down some. How much, I'm not sure, but the magnum will be hotter. I'd say somewhere around .3 to .8 grains less powder.

Thanks Chad.

You're welcome! On a rifle round, going to a magnum equals about .3 to .5 grains less powder. But in such a small pistol case, I'm not sure. I have not tested this.