I'm betting it had a lot to do with those heavy slugs. I've only used RB's in mine, but with charges up to 140 grains of 2f it's never come close to hurting. It's no pussy cat, mind you, but perhaps due to the cast off in my rifle and positioning of the butt on my arm, it's really not uncomfortable at all. But I probably only shoot one round from the bench for every 1000 offhand. Come to think of it, LOP might be a question too, because mine is a little longer than usual and "fits" my 6'4" frame better than any other hooked butt I've shot.
I'm sure with you on the heavy recoil. I'm not particularly bothered by it, but some guns and stock styles just hurt more than others. I still miss the 458 2" I built back in the 70's on a lefty Carl Gustav action- feel like a fool for letting it go. But I've got an original 450 Alaskan built on an M-71 Winchester that's fairly light, but really enjoyable for me to shoot. It too is a little long, and though I can seldom keep my front foot on the ground when I light it off, it doesn't hurt. Folks not as tall who shoot it usually only do so once, then complain for the next ninety-leven years about the recoil. In truth it doesn't bight me nearly as much as my 458 Winchester.
Then there's my "carry" 375 H&H. It's really sweet for packing all day long at 7# including the scope, compared to my 9.5# "hunting" 375. But lordy, you sure don't want to shoot it from a bench. Oversize butt, straight stock, recoil pad and all, it has given me double vision with just three shots with 300 grain factory loads from the bench. When I'm sighting it in or testing loads, I stand fully upright and rest it over the cab of my truck. Rock and Roll Time!!!!