I have been playing with loading shotshells for 410 using 444 marlin brass, and this is how they look....
I discovered that my 7.62X54 sizing die will slightly size down the fired brass and can be used to put a nice rolled crimp on the case to hold the overshot card in place. This is loaded with a large rifle primer and wc820 powder and there is a 410 plastic wad holding about 1/2 oz of shot. The over shot card is a 7/16" disc cut from a translucent plastic lid that I had laying around.