Rifled or unrifled; see what it likes. Look for accuracy and don't worry about one brand of slug having more "knockdown power" than another. My Rem. 870 is my dedicated slug gun and uses 2 & 3/4" Winchester/BRI sabots. Its had a fully rifled barrel since about 2001, before that it had a smoothbore slug barrel that really preferred 2 & 3/4" Winchester foster style slugs. Prior to 1987 it was my old High Standard Flite King with 2 & 3/4" Remington Slugger foster slugs. I went through one phase with the 870 where I felt like I had to use 3" magnum slugs for more power, even though they weren't quite as accurate as the 2 &3/4" slugs. After a while I noticed that deer couldn't tell the difference; they expired just as quickly from either a 2 & 3/4" or a 3" slug. So I finally realized that any slug can cleanly take deer at any normal shotgun range as long as you can put it where it needs to go. That's why I stress accuracy. Took the biggest whitetail buck of my life back in 1989 with that 870 smoothbore barrel and 2 &3/4" Winchester foster slugs at almost 100 yds. ( 85 to 90 actually) but I had practiced at 100 yds and knew how high to aim because they sure drop between 50 and 100 yards. But even at that range they work on whitetails if you hit 'em right. Accurate slugs = venison in the freezer.