1885 High Wall pressures

I recently met a fellow who has an original 1920s manufacturer Winchester High Wall in 45/90 and he is shooting some questionable (to me anyway) loads in this thing. Using 500 grn jacketed bullets and H4198, not sure about the charge, that thing not only kicks painfully but hard extractions are common however he is writing this off to an extractor problem. I just met the guy and could say little except that it looked to me as if the loads were a bit hot and that it might be a little too hot for an old gun. He assures me the rifle can handle anything a new High Wall can but IMO there is soon going to be an accident.This however does raise a very interesting question to me and that is just how much pressure can an original High Wall handle? The reason I ask, and the reason I became acquainted with the guy I mentioned, is because of a 45/90 High Wall replica I hope to have soon. I certainly don't intend to "hot rod" my rifle and BP load pressures will be just fine with me however I do want to use smokeless if I can keep the loadings within a safe and sane range.