[Elderberry]

My FIL hunts duck with a 10 gauge. It is subsonic and the loudest gun I’ve ever heard. I can hear him at pond almost a mile from my house shooting duck.

Your FIL's duck loads will exit the muzzle supersonic but will be subsonic by the time they get to the ducks.

http://guide.sportsmansguide.com/ballistic-chart/wballistics_192.html

[central_va]

I don’t know much about shotguns about a 10 gauge is incredibly load.