I had one that was my primary deer shotgun for over a decade when I lived in an Ontario shotgun zone. I tried a number of assorted sabots, all were pretty good but the best by a significant margin were Winchester Partition Golds. I sold that gun when I moved into a rifle zone in 2011 and haven't used a slug shotgun since, so I have no idea if those cartridges are even still manufactured.
That gun/cartridge combo was a very consistent 200-yard deer gun, a better shooter than some other slug guns I had that cost 2 or 3 times as much. As I recall, it had a pretty decent recoil pad straight from the factory, and also came with a heavy steel cylinder in the buttstock as well, which added weight to help with recoil and also acted to balance the gun nicely. Without the weight, the very heavy-walled barrel made the gun pretty poorly balanced. It's the only one of several rifled-barrel slug guns that I kinda wish I had kept.
If you experiment with a few different Foster-type non-sabot slugs, you may find one or two that shoot very well in the rifled barrel on the H&R. Challengers and Federal Truballs worked really well in mine; Challengers usually printed three big holes into a 4-5 inch circle at 100 yards.
