That would be an excellent load for the Browning BPS 16 gauge, which is built on a modified 20 frame but still towards the heavy end of the spectrum. I suppose fine for some of the Remington 16s which were built on 12 gauge frames.
Would exceed the proof of many 16 gauge game guns (including mine).
Ive no experience with the Winchester M21 but perhaps that would have been a good strong 16 load for open water ducks, late season pheasants, turkey, and other birds where youre waiting a long time and only taking a limited amount of shots per day.
