I ran 4 boxes of hi brass 3” max bar #4s through my synthetic stocked 500 several years ago in less than 30 minutes...i was sore but i was also used to shooting a hot loaded 450 marlin so hey ,just a bruise that will heal.
To the orginal point...my father in law used to go dove huntimg once a year and they’d all have their fancy guns and a case of shells, he’d carry his 20 gauge coach gun (imp/mod cylinders) and maybe a box of shells and get his limit with a few left over every time
20g is fine for birds. In fact, I’m looking for a good one, prefer double barrel...but those are rare anymore.
But an 18in 12g with 3in mags/00 is for a different kind of shooting.
And I’m not interested in shooting 20 rds through it just for fun.
And I’m a big, strong man.