I have a Weaver mount on my 30 Carbine Blackhawk. I mounted it years ago and had taken it off once about 5 years ago to go back to open sights. I had it off for about six months and went back to the scope because it's a fun round to shoot at long distances. I also switched scopes from a Bushnell 3-6X to a Simmons 4X. Both scopes work great and really, if you're not resting the gun, you don't need 6X on a revolver.
What I was most concerned about when mounting a scope to a revolver was leaving any kind of marks on the finish. I was relieved to note that NO MARKS were left on the finish of my revolver when I had removed the scope mount.
I'd recommend the Weaver base for a Blackhawk. While the 30 carbine is short on recoil and might not be representative of a big bore vs. scope mount, my mount has always remained stable and true. I've never had a problem with it nor scope adjustments etc. I would think that your .357 mag isn't going to produce that much more recoil to worry about anything coming loose etc.
By the way, if you're wondering how it mounts; you'll have to remove the rear sight and screw the mount into the sight mount opening on the top strap. Also, there is a barrel type lug or attachment that runs half of three quarters around your barrel. I placed "mole skin" on that before I mounted it in order to prevent any scratches or marks on the finish. I realize that one shouldn't use something like this as it might hinder accuracy but I have not noticed much of a problem as my Blackhawk shoots 3.5 to 4.5 inch groups repeatedly at 100 yards. I don't expect much better from a standard, run of the mill, non-custom revolver, not to mention that it's fairly old and has seen a lot of rounds through it.
