Recently did a test with std vs magnum primers in lighter loads in.357 brass.Essentially 38 Sp data.Using a S&W, 6",686.
I found a powder with magnum primers gave better accuracy than flake an another powder gave better accuracy with a flake powder.
In the 4.6 gr loading for both,158 gr SWC cast or 158 gr RN cast I used W231, std primers and Universal Clays, magnum primers. Each gave the same accuracy as well as I could shoot. Not so though if I switched the primers to the opposite powder.
Universal Clays as described is not a ball or spherical powder, but is a finer cut than W231. Many reloaders call it a ball or spherical powder.
Not scientific data, only what worked for me.
Last edited by saddlesore; 04/21/21.
