Hello azmike,
It is true that the Contender in .45-70 can only go to 28,000 cup as told to me by T/C Arms. Don't let that get you down though.
The IMR reloading manual lists a 405 grain cast bullet at 1706 fps with 48.5 grains of 3031 (21,100 cup). The Hodgdon manual lists a 300 grain hp at 2221 fps with 55 grains of H4198(27,600 cup). If those loads aren't more snort than you need, you better buy a Ruger #1. I can attest to the recoil produced by loads less hot. It will get your attention! Happy shooting azmike!
Jeff