I'm a black powder buff myself.
Have about 40 pounds hoarded in the out building.
The way out back building.
Shouldn't be much trouble to clean up a Contender after using black.
I also have the 23 inch conender 45-70 as well as my 1895 Marlin LTD II with 26" taper oct barrel.
Nice shooting rifle with an originl n.i.b. El Paso Steelite Weaver 4X on her.
I'm taming the Super 14.
Today I picked a moderate load using 30 grains of SR4759; the books idicate about 1600 f.p.s.
That may be enough, shooting was not painful at all.
Might work up a little as I go.
Have to try 4198 and Re7 and 3031 also.
I shot the 300 grain Sierra into water jugs at 25 and exploded all of them but the last one.
Only found little pieces of lead and copper.
Made one heck of a water mist gyser too!