I think the general consensus is that magnum primers should be used with ball powder. I use std primers in all my 357 and 30 carbine loads with 2400, which isn't a ball powder.

I think W231 is a ball powder so maybe that's why some manuals call for mag primers.

Personally I don't think I've ever heard of anyone using std primers having any problems with W231 to load .357.

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