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Ive been asked to make some for a mates bolt action garden gun
410 will probably just load up some 38-50 brass (aka) 38-303 with forming loads and just fire them off

Ive fireformed 303 British to 410
Works great
But a forming die is definitely a better way to do it

I form my 38/50 rem hepburn brass with just a 375H&H expander ball installed in my lee...