We've strayed just a little bit from gundownunder's original inquiry about knuckle busting recoil from a .357 Magnum, but I don't think any harm's been done. Bob, I suspect that most serious handgunners no longer find the recoil from a .357 Blackhawk to be abusive, but that doesn't mean that some people won't be bothered by it. The first thing I'd suggest would be to tighten your grip a bit. Not white knuckle, trembling tight, but FIRM enough to slow the gun's movement toward your knuckle.
In my own case, I'm not bothered by knuckle busting, even with the notorious square back Super Blackhawk trigger guard, until I get into the .475 Linebaugh and .500 WE with full strength loads. They can make my knuckle take notice in a hurry!
Like others have suggested, I've tried band-aids and shooting gloves on very heavy recoiling guns. They can work well, but I finally abandoned them for a couple of reasons. I found the band-aids to be a bit of a nuisance, coming off when I most wanted them.
Gloves? I have short fingers, and with most shooting gloves available today, the padding is heavy enough to increase trigger reach, which made me reposition my hand a bit, and had the effect of actually loosening my grip. The old Chimere glove, which I used for many years, did not have padding that thick in the palm, but alas, it's no longer available, and mine finally disintegrated several years ago.
A couple of years ago, I found the solution that works for me. I'd been given a pair of Past shooting gloves. They're too thick for my taste, but I used them a bit on my .475's and .500 WE. Then one day I took the left glove and cut the middle finger off it.I slip that padded middle finger ( It's really only a partial finger, terminating between the first and second joints) on the middle finger of my right, or shooting hand. The padding prevents any knuckle busting, it's easy on- easy off, and it's been quite durable. I now use only this "knuckle guard" to my complete satisfaction, and my shooting glove is gathering dust somewhere.
Perhaps this will give you or someone else an idea. The " finger" need not be from a Past, there may be others that will do quite well.