Reloading data seems to give a false answer to this question. Also, intuitively, I've always figured that since cast lead seals a barrel better, then the pressure for any given load of powder would be greater with a cast bullet than a jacketed one of equal weight. I'm just wonderin' what you guys think. If I load 54 grains of IMR4064 pushin a 405 gr LRN 45/70 pill, will the pressure be less or greater than the same load pushin a 405 gr JSP (this is a near max Marlin load for the JSP)? If what I been hearin' is correct, the only consequence of this experiment will be a leaded barrel, since pressures are bound to be less.