I bought my daughter a 20 ga several years ago. She shoots 3" Kent faststeel. I shoot a 3.5 12 ga. I also use Kent. Our last hunt she killed about 3-1 over me.
No reloading for me. My son uses either Hevi X or Hevimetal shotgun
shells in his Mossberg 20 gauge. He has take Cans, pintails, mallards,
etc with zero problem
I shoot a Weatherby SA-08 20 ga. with Fiocchi 7/8 oz. #2 steel and it does very well out to 40 yds., but I would definitely consider that to be the maximum range for that load.
I do not reload shotguns for steel. I use Hevi-Metal 20ga 1oz #3 shot. I am finding myself using the 20ga more than my 12ga due to weight of gun, recoil, and quick handling. I am running a Benelli M2 in both the 12 and 20ga for waterfowl.
The Hevi X 20 gauge shells were amazing for my son last week
in Arkansas. He was able to shoot his limit each day cleanly.
I also want to suggest that if anyone is looking for a shorter
stock shotgun for a youth hunter or lady hunter check out
the Mossbery SA-20's.