Randy,
I think there's two limits for lead. One is a rotational problem, the other is plain velocity.
I've read posts from people who noticed lead dust on the bench in front of their gun. They concluded that the rotational spin from the rifling at that velocity was too much for plain lead. I don't remember if they tried a slower twist at the same velocity or what. There won't be a "set limit" for rotation and pure lead because this will depend on the caliber and velocity.
The other problem is the struggle to get soft lead to plow through the atmosphere at such velocities. If you don't think this is a problem just look into aeronautic research, one of the difficulties they have with jets going Mach 2 and Mach 3 is overheating of the leading surfaces due to air friction. 2200 fps is roughly Mach 2.
I can't imagine there would be a set number for this factor either. I would guess that bullet shape has something to do with how well it resists air friction. Perhaps a spitzer point bullet could achieve an extra hundred fps compared to a flat point. I will also speculate that ballistic coefficient could play in here too. A bullet with a poor BC will slow down faster. That bullet won't be subjected to high velocities for as long a bullet with a high BC. A round ball pushed to 2300 fps might survive better than some conicals at same speed because the rb will drop below 2000 fps in short order.
In short, Randy, I don't think a concrete limit is out there. At least not a generic one. You might be able to find a limit for each individual bullet from a specified twist.
Now, more towards the point here and that is trying to bring the cost of muzzle loading down.
I'm not saying that there is something functionally wrong with the sabots. I'm just agreeing that sabots are a significant part of the muzzle loading cost.
Which do you think costs more? A pack of sabots or a sheet of paper?
Now, if you can get similar performance using paper jackets - you will save a bundle of $.
Of interest, I didn't get squat for accuracy with paper patched bullets until I started loading higher. The reason was the paper jacket needed the hot charge to obturate the bullet and get a better gas seal. Once I put enough powder in, I immediately noticed larger chunks of paper exiting the muzzle and the groups shrank to something more reasonable.
I think the biggest hurdle with paper patching a muzzle loader would be caliber. Paper jackets use bullets that are closer to bore diameter. That means a .50 will use something like a .495 bullet, not a .45. That might get a little tough to push up to 2200 fps. However a .45 muzzle loader has more promise.
And in Wisconsin it's legal to use a .40 caliber muzzle loading rifle. I would think that it would be reasonable to get a .40 paper patched bullet to reach 2200 fps.
You might want to try paper patching with some really heavy paper. Then perhaps you could achieve the same effect as a sabot, that is use much smaller bullets. Say two wraps of heavy construction paper might bring a .45 bullet up to .50. I don't know.
Or, since you're muzzle loading you could use cross-patching. Just lay two strips of paper across the muzzle to form an "X". Then seat the bullet just like you would a patched round ball.
