I shoot slug myself, but have never found those blade foresights conducive to more accuracy than a fibre optic bead, indeed, throw in a decent rear sight such as those used in turkey sights and I will happily put lower profile sights against ghost ring and blade at a hundred yards. More importantly, I find the bead means I can still shoot fast and instinctively with foresight only on moving targets. Each to their own of course, but I have never understood trying to turn a shotgun into a rifle. If you want a rifle, take a rifle. If you want a big 500 grain bullet, take a 45-70 guide gun or similar.
I hear you on that.
Nevertheless with the Mossberg I can put out five chicken dropping shots much faster than I can with my Dan Wesson .44 with 310 grains - and I was considered a lot more than expert with that, and it's just under the 4lb limit for an IMSA revolver - fully worked and national class.
A 3" magnum slug out of a light shotgun is the same as shooting a .375 300 grain out of a Winchester Alaskan. But the Alaskan is far slower to bring to bear/use and far far slower on repeat shots. Mine now has a worn out barrel which is a pity because I did a full glue job so it could manage our climate - so I do shoot one well. Anyway that's what I have to sleep with now for a while, and I'm sure it will work.
The big point is that I've long been well under 10 feet on a griz and we were all surprised. Close up on a black and I had to back them off, as they were trying to get me to run. We all lived another day.
I would always carry the .375 with heavy Barnes bullets or A frames when we took out little kids, because I was always super cautious then and would have dropped anything which looked threatening at range and which didn't run at the warning shot. I find the .416 Rigby to be too much kick for repeat shots and too much muzzle flash with any loads at dusk - otherwise I'd have one.
I've seen so many people with guide guns who carry them as a token or talisman of survival. Same kick as the slug gun or .375, but the people will not shoot until they master one. Seeing a regular person shooting one at targets is so sad. They are good, just so slow to bring into action and for repeats. And I was expert in cowboy silhouette with everything. I used a 30-30 rifle (long barrel tricked), but I have used everything and we'd haul out ammo by the brick. I've shot 200M chickens with a long 45-70 but that sure takes lots of practise. Go swimming with one as when you are using one for protection while fishing, and you'll see how a lever might open snag and kill you.
Now my grandson knows how to use and trust the old rifle sights on the Mossberg. Next step is that he has to carry it while wading and fishing and soon learns to see that pistol grips and extra shell carriers will drown a person if ever they get swept to a sweeper or log-jam and snag. I've had almost as many close calls with those as with bears. He just got his bronze so he should come out OK. The gun has seen all that sort of abuse for decades. I know it's all controversial stuff - but I gave my grandson my slug gun to use because it works now he can use it. If I worried about it working, then he'd have the .375.