The biggest difference is in shot weight difference. Twenty =7/8 of ounce in shot and 12 is an ounce and a 1/8 of shot. But in the end nobody asks how? Just how many!
I traded my Marlin 30-30 lever gun straight across for a brand new Mossberg 500 20ga Youth Model. I liked my Marlin but after experimenting with pointy bullets in it and their superior performance over the normal 30-30, 1 in the chamber and 1 in the magazine just didn't do it for me. I found a 30-30 bolt gun at a gun show not long ago for next to nuthin' :thumbsup: :D:D