If you check out some of the loading data for that caliber, you'll find that some pretty low-pressure loads for 249 grain cast bullets will exceed 1300 fps. I agree with Ranger44. 100 Y.0. steel in a fine rifle like your Marlin needs to be respected, and greased lead alloy bullets are a lot easier on old barrels than new, jacketed ones. Generally speaking, just as deadly on game animals, too.