To the OP: Nice gun you got there, and that's about as good a price as you're going to find. Good deal. I like that sling. Can't say much for the snow though. Brrrrrrrrrr
A slug barrel is far from ideal for buckshot.
This is the truth, although you'll often read/hear experts say otherwise. Back in the day, everytime the subject of buckshot came up in a magazine or a book, there would be some "expert" telling us to use open chokes and the biggest buckshot you could find, and limit your range to 20 yards or so. Those same "experts" would usually admit that they had never hunted with buckshot, which I always found interesting, Well, that hasn't been my experience.
I suppose if you want to use buckshot for SD/HD, an open choke gun is just as good as anything else, the ranges aren't that long, but if you think you might want to reach out a bit, get a barrel with some choke in it. Every gun is different, so try different shot sizes but I don't ever remember anyone shooting 00 for hunting. I'd say 75% of the men I hunted with used No 1. The others used 000.
I bought a Sears/Mossberg 500 with a 28" mod/24" slug barrel, years ago that the original purchaser had returned to Sears because he said, the slug barrel didn't shoot buckshot well. I wasn't surprised by that. I took the gun home, stepped off 40 paces (call it 30 yards) and put 17 of 24 No 1 buckshot (3" Remington shell) into the bottom of a bushel basket (we weren't too sophisticated in those days) which is about 15-16 inches in diameter. One shot. That was plenty good enough for me. I never used anything but 3" Remington No 1 buck in it. That was a deer killing shotgun and has served me well for years.
I don't think I've ever used that slug barrel.