i second the 3 inch accutips. I had a open sight Mossberg barrel for an 870. shot everything well, mainly win platinum tips and hornady sst. 3-4 inch groups at 100 yards were the norm, open sight. win platinum tips were my favorites, dam good slugs, now discontinued. open sights and low light conditions don't go together so I sold the barrel and bought a Mossberg barrel again but a cantilever mount barrel. tried win platinum tips, partitions, hornady sst, the federal barnes slugs, all in 2.75 and everything shot 8 inches at 100 yards for the whole box(5). I was not too happy. read somewhere online that sometimes due to the way a chamber is cut some will shoot much better with 3 inch slugs. rem accutips were new and just coming into Canada so I got a box. put all 5 into less than 3 inches at 100 yards. every year before the season I shoot a group at 50 to make sure shes still on, its 1 to 1.5 inches, more often than not all 3 touching. last year I tried a box of the new federal trophy tip in 3 inch and it was over 3 inches at 100 yards so im simply gonna stick to 3 inch accutips. never tried the 2.75 inch accutips, maybe I should.
shot a buck that was almost straight on this winter, he was ever so slightly quartering. 60 yards, put it right in his shoulder found the beautifully mushroomed slug right in front of his opposite side rear ham. he fell right down, kinda slow motion. ive shot a bunch of deer with sabot slugs, from an accurate gun there very very lethal.
word of advise though, don't trust the factory ballistic tables. real world velocity is often much slower then the long barrel the manufacturer used to test. my groups fall apart after 150 yards. at 150 I will kill my deer every time. at 200yards they don't even stay on a sheet of paper. they must go subsonic somewhere shortly after 150 not after 200 like Remington would have you believe. do your own testing to see how far your gun will hold a tight group.