i've made my own .357 mag shotshells for yrs... i took an old .38 spl case and sharpened the case mouth with my case deburrer... then i used the sharpened case to cut wads out of plastic lids off butter containers and such.... you can get alot of wads from one old lid.... then you prime the case, put in about 3 grs of bullseye,put a wad over the powder,push it down to the powder but do not compress it, put shot in the case up to the case mouth, put another wad over the shot, and then crimp the case to hold it all together... i've had real good luck making them this way....... they seem to patern pretty good too........