A couple more points here....
a. If a shotgun fits you ....there shouldn't be any bruising to your shoulder or face, etc......unless you're doing something very fundamentally wrong - with the mount or execution of the shot. I'm a clay target shooter ...and in a 12ga where my loads are not powder puff loads ...but 1 oz at 1225 fps ...I can easily handle 10 boxes a day ...if I'm doing things correctly. ( and I'm in my 60's with a completely rebuilt shoulder and only half a bicep in my shooting arm).
b. Practicing with what you consider a Defensive shotgun ...on clay targets is a good idea ...because its an easy way to practice sucessive shots ..at least 2 shots anyway ...on a number of target presentations. Now if your defensive shotgun doesn't have changeable screw in chokes / and you have just an open Cyclinder choke in the gun ...you can compensate a little to tighten it up by shooting 1 oz or 1 1/8oz loads of 7 1/2's vs 8's or 9's ....and even though typical OO Buck loads are often heavier payloads at faster velocities that "clay loads" ....you can run some loads like Remington Nitro Sporting clay loads 1 1/8 oz of 7 1/2's at 1300 fps ...thru those guns and they'll give you some "pop" as well ...and still be legal to shoot on a clay target field ( most clubs won't let you go any bigger than 7 1/2's -- because of safety on their ranges ).
This is a typical Remington OO shell....
12 Gauge, Remington Express Buckshot, 2 3/4", 000 Lead Buckshot, 8 Pellets, 5 Round Box, 1325 FPS.