You cannot safely use heavy rifle loads in the .45-70 Contender. While it is generally assumed to be safe to use loads developing up to about 30,000 cup, you will likely quit before you get there due to recoil. Loads listed for Trapdoors will be safe enough; some of Sierra's Contender data is close to their M1886 rifle data.
For deer hunting and general practice, the 300-grain bullets from Hornady, Sierra and Remington work well, giving good killing power in max loads with lower recoil. 400-grain bullets can give good accuracy with mild recoil over 15 grains of Unique, but top charges of IMR4198 will really get your attention.