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I then loaded the casing with 3.9 Grains of clays and 4 38 caliber round balls 82 grains each. Plus some felt pads that I bought from Canadian Tire. The second firing with the lead balls blew the casing out to fill the chamber.
The balls that I had casted stayed in place with just friction/.
Please note that no gunnutz were harmed during any of these experiments. Also for anyone thinking about making a cartridge with a regular bullet for a 410 it probably will not work. I spent 50 bucks in a mold and 40 caliber factory crimp. The crimper ruins the 410 casing and a 39 caliber bullet necessary to pass though the choke will not remain seated in a 410 casing. Been there done that.
jasonburnsdundee, a few questions for ya. Did you anneal the brass before you fireformed the brass ? And if the 38 cal. balls stayed in place with friction why wouldn't a cast .390 bullet ? What did you do with the mold that you bought ? Jack