Disclaimer: Use the following information at your own risk. We went through this during the "Great Component Shortage" where SP primers were scare and some reloaders had to resort to using SPM/SR primers for pistol loads. (And no, none of the members reported their guns "blowing up" ) Due to larger primer flash size and duration SPM/SR primers produced, many reloaders reduced powder charges and I would do the same if I didn't have SP primers to use but had SPM/SR on hand. As to those worried about SR primer cups being harder, I tested CCI SR 400/Tula SR/Tula .223 primers in my Glocks and didn't have any issues igniting them - https://www.thehighroad.org/index.p...ts-your-experience.630512/page-3#post-7806985 And in a recent thread, a member tested Winchester SR primers in .38 Special loads and they all fired in Taurus 85, S&W Mdl 19 and Henry - https://www.thehighroad.org/index.p...-primers-for-38-and-357.865932/#post-11444530 BTW, here's more info from CCI "allegedly" but since it's from the "internet", use it at your own risk - https://www.ar15.com/forums/armory/...ech-About-SPM-vs-SR-Primers-Today/42-282516/? "I called ... [CCI] to discuss the technical differences between their primer types ... asking about the cup thickness, formula differences, and formula amount differences between their #500 (SP), #550 (SPM), and #400 (SR). She had me hold a minute to get the detail specs up on her screen and this is what she said. Cup thickness: The #500 has a thinner cup than either the #550 or #400 which both have the same cup dimensions (including thickness). Flash powder formula: All three sizes use the same formula for the flash powder. Flash powder amount: The #500 has a slightly smaller amount (3 micrograms) than the #550 or #400 which both have the same amount. I asked if the SR primers could be used as an acceptable substitute for the SPM primers. She compared the #550 and #400 and then replied that yes, they appeared to have the same specs, same dimensions, same cup thickness, same formula, and same amount. She even noted that the SPM primers were slightly taller than the SP primers and were spec'd the same dimensions as the #400."