Small pistol primers Magnum vs Standard

I'd start lower than 2 tenths of a grain, down at least to mid charge and work up from their.

The "magnum" small pistol primers probably have thicker cups than the "standard" version.

I have swapped magnum and standard primers in .223 ammo, and I have found there to be no difference whatsoever in velocity. Magnum small rifle primers are definitely thicker than standard small rifle primers.

markb said:

I have a lot of CCI 550 Magnum pistol primers and would like to substitute them for Standard primers. The 9mm load is 5.5 WSF, 115 gr. JHP. The load is about .2 grains under max. Should I chuck them or can they be used safely?

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The rule of thumb is to back off your charge .5gr (10%) and work your way back up. Be sure that your hammer spring has not been lightened up. The thicker Mag. cup demands a strong hammer strike. BTW, with the advent of primer shortages, I have been using Remington 6 1/2, Small Rifle primers, in many of my small primed handgun loads, with complete satisfaction!!

I used the CCI magnum primers last year for a bit when I couldn't find regular. I tried them with two different 9mm loads. One was with Titegroup and Rainier bullets the other Solo1000 and Precision bullets. I compared these loads with SP primers and SPM primers and found that across the chrono they were identical. The primer used made no difference. Your results may vary so work up as recommended.