Bought a new ported Katahdin barrel. I have several hundred 300 grain JHP .458 bullets. I have looked at 4-5 web reloading sites and about the same number of reloading books. I would appreciate feedback on what powder and charge to use for whitetails. I am an experienced reloader, but new to the 45/70, much less the 18-inch barrel. I have four other Encore barrels and two frames.