It's funny how you don't even feel recoil when you're shooting at a deer, but when sighting in, well that's another story. I mounted a scope on my slug gun this year, and went through about 5 or 6 brands of slugs to see which was better at 100 yards. Staying focused isn't easy when you know you're going to get pounded every time you press a shot off. I put a bag of shot (25 lbs) between my shoulder and the recoil pad to help soak it up, and it looks funny but it works.
For me, my old favorite Active slugs still shoot into about 6 inch groups at 100 yards, but they're getting hard to find anymore. The new Remington BuckHammer slugs shot pretty good, along with the Lightfeld white box slugs. Both gave me about 5 or 6 inch groups at 100 yards. Next was the old, cheapo, foster style Winchester slugs, and the yellow box Brenneke slugs delivering about 8 inch groups. The other high-dollar Winchester Supremes, and Remington Copper Solids didn't do as well, and shot to a much, much lower point of impact, probably due to their higher velocity. Since they cost over $2 each, I'm not to sad that my slug gun doesn't like them.
For me to get any better groups, I'd have to somehow mate the barrel to the receiver permanently, but I really don't want to do that. It took me a long time to decide to drill and tap the receiver.