I can't speak for all 512s out there, but mine will shoot Brenneke KO SABOTS (not the standard KO Slug) into a ragged hole at 50 yds. These are 1 oz 63 caliber (20 Ga) slugs moving at about 1650 fps. Winchester BRI style sabots are very good as well. I tried some Hornady H2K sabots and they were all over the place. So I'd say that the 512 is best for sabots in the mid velocity range, as opposed to those approaching 1900-2000 fps.
The gun itself is not going to win any beauty contest. It is bulky, and carries more like a 2x4 than a rifle. But it is a repeater, and for that reason, plus the accuracy (of mine at least), I'd favor it over the H&R. I've shot a bunch of deer with my 512 and I have needed a quick second shot a couple of times. I'd have lost at least one deer if I was shooting a single shot.