With the size and weight of the Bone Collector and the eye relief of the Leupold 2x20 pistol scope you would have to be pretty committed to getting hit in the face for it to happen. You're not going to get face smacked even with .460 Magnum unless there are unique circumstances such as being brand new to firing big magnum revolvers.
Anyway, if you need to, go out the first time with someone experienced, and start with lightly loaded .454 Casull such as Federal Premium 250 Grain (1,530 FPS) Barnes XPB at 1,300 ft. lbs.; or lighter yet, Cor-Bon Hunter Ammunition 240 Grain (1,400 FPS) JHP at 1,100 ft. lbs.; and then work your way up to the 454 and 460 plus 2,000 Ft. lbs. stuff if you want or need to. If the OP's needs are limited to 100 yards, it's hard to think of many cases in North America where light to medium loaded .454 Casull wouldn't be enough. The lightest .454 Casull starting point I'm aware of is Winchester Super-X 250 Grain (1,300 FPS) Jacketed Hollow Point, with a .44 Magnumesque 938 ft. lbs. In fact, it should kind of be like shooting a .44 Magnum, only less due to the big X-Frame. I'd love for someone to post who could tell us.
The eye relief on the Leopold 2x20 is 18"; on the 2.5-8x32 it is 15". I have experience with the 2x20 and I love it, and it holds your zero flawlessly. When Leupold claims shock-proof they mean it. Not quit as much with the Burris, but then I don't have experience with the Burris HD.
I would have recommended the Leupold 2.5-8x32 except that unless I'm mistaken, the OP just needs this out to 100 yards. If that's the case, the 2x20 would seem to me to be an excellent solution.
I would also recommend considering field of view. With the 2x20 is an adequate 21'. Perhaps one argument in favor of the 2.5x32 is the 37' FOV at 2.5X, and even at 8x, you still have a 13.5' FOV. So even at 4X you're left with a very nice FOV with the 2.5-8X32
My big issue with the 4x28 is the ever-so-narrow 9' FOV.
