Ned, you need 30 rounds. Targets are 15 third scale steel bison scattered between 100-300 yards. You get 15 shots to knock them down. Then everyone moves back 75 yards or so and try again. The 50-70 is excellent for this. No sighters, no posted range. Guess your settings and shoot. I set for 200, started on the near ones holding low, then held higher as I moved back thru the herd.
Big bore single shots. I don't think BP is mandatory, but it does give best performance for the conditions. Them things weigh 60+ lbs, ya gotta load heavy! I'd say a 45-70-405 is marginal/minimum with 500 grains far better on the critters. They have to go down. Pretty much everybody shot seated off cross sticks.
It's a slow paced, one guy at a time event. Bring a chair, binoculars, a canteen, and good conversation. A fine way to spend a day!