I had MGM make me a long throated 15 7/8" 45-70 fluted stainless bull barrel with their integrated tactical muzzle brake. The hot loads are just under 3,000 ft/lbs with the Barnes 300gn TTSX. It's a hoot to shoot and very manageable with +p loads, but at your rate, an hour of loading would be many years worth of shooting.
What types of bullets do you like for the 450? The Barnes are pretty $pendy for plinking and the Hornady 300gn interlok hollow points pattern rather than group for me.