Star1pup
"]On another forum I've been trying find out just how different .357 mag & .38 spl loads are for my rifle vs a handgun. I have heard both that handguns are stronger than rifles and not to use handgun data for my rifle and that the rifle is stronger and I should be careful not to use a rifle load in my handgun."
This is a classic case of a fact for a particular situation being repeated out of context until it becomes urban legand or an old wifes tale. Heavy +P or magnum type loads should not be used in the M1866 or the M1873 replicas. These two actions are not strong enough for the heavier revolver loads. However, your Marlin, the M1892s and the M94s are quite strong enough for the heaviest +P and Magnum .38 or .357 revolver loads. Ricciardelli is correct; load for the rifle (not exceeding any revolver loads) and then use it in the revolver.
Caveat; those with .45 Colt rifles and revolvers. Do not exceed loads in the rifle that are for your particular revolver. Example; DO NOT load heavy Ruger or FFA revolver loads which will be safe in M92, Marlin and M94 rifles, if you have a Colt SAA or one of it's clones.
Larry Gibson