A word about pistol bullets at muzzleloader speeds.
I've long thought, and my experience proves ( so far), that these bullet hold together better than expected due to their jackets being in perfect condition, due to the sabot, and not compromised by rifling.
I've shot deer with 180 and 200 grain .40 caliber Hornady XTPs at velocities up to 1800 fps, from a .45 caliber Black Diamond. That is well above their ratings, especially the 200 grain, and got pass throughs in all but two. One was a 200 grain that left at 1800 fps ( chrono'd) and hit the shoulder ball and a rib on a big doe at 12 yards. A quartering to shot, she hauled up her landing gear and dropped. Her chest was... gooey. The Hornady didn't exit and couldn't be found.
The other, a broken rack 8 pointer, was kinda bent when I shot. Got a rib going in, totalled the lungs and liver and, LORD only knows how, wound up under the hide on the outside of his right ham. Sans jacket, but still weighing 131 grains. That 180 grain left the muzzle at 1700 fps. Chrono'd. It was a 50 yard shot. He went 50 yards, all wobbly and leaking badly, before giving up the ghost.
I have no scientific data to back this theory up. But if you look at slow motion bullet impacts, you see the jackets rupture along the rifling grooves before it all goes to bitty shards. Perhaps no grooves means it holds together just a little better?