I was watching a hunting show the other day, this guy in Wyoming, I think, was hunting Buff with his Sharps replica in 45-70. He mentioned he was using 400gr bullets but made no mention if they were factory or reloads and no mention of velocity.
They also never showed where he hit the buff, but it took hin FOUR shots to drop it. Extimated weight was 1800-2000lbs.
One noted point, all but the last shot were on a trotting buff. Like I said, I have no idea where he hit him. The buff didn't even act like he'd been hit on the first three shots. He claimed to have hit him with all four and the guide said "good shot" on 2 of the 4 shots.
Overall, my impression was that sometimes they will use anything to fill up airtime.