the 5 1/2 are magnum primers. i have use them in 40 s&w loads. they give me about 50 fps more than the 1 1/2 primers. i ran several test loads across my chronograph before i went full time with them. i dropped the same powder load for both of the primers. i don't load my range ammo hot, i load it under factory settings. that why a chronograph is a good thing to have.
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