The Slugmaster was kind of the "last hurrah" for the venerable ols Mossberg bolt action shotguns. They represent an old design being revived for newly developed markets, i.e. scoped slug shotguns. Bolt action shotguns kind of disappeared in the 1980s, only to reappear in the 1990s as slug guns after Browning 12 gauge A-Bolts and Tar Heel Hunters were marketed and gained a reputation as accurate long-range game getters. I would not count on a Mossberg Slugmaster being accurate or durable, and I am not even sure if they had rifled barrels or not (I believe they were smoothbore). They were a cheap shotgun sold by a company with a reputation for cheap shotguns, and were not modified in the manner common to long-range slug guns. If you want a long-range slug gun, get a Savage 220 or a Browning A-Bolt 12-gauge.
Once upon a time, bolt action shotguns were the economy repeater, not really intended for the "yeoman's duty" of hunting all the time. When I was younger, they were sold as "goose guns", something to be carried along duck hunting just in case a goose passed within shotgun range of the blind. I do not remember dedicated goose hunters when I was young, just opportunistic hunters that would take whatever came within range and the capabilities of their firearms. A separate shotgun loaded with BB shot (instead of the #4 or #5 typically used for ducks) would take care of any opportunities.
Never try to educate someone who resists knowledge at all costs.
But what do I know?