One of the hardest things to learn about shooting a muzzleloader in field positions rather than off a rest, especially offhand, is the importance of "follow through" or what happens after you pull the trigger but before the bullet leaves the barrel. Your gun can move a long ways off the perfect aim that you started with, and as a result you miss. It's important in modern cartridge guns too, but it's critical for the slower speeds that everything happens with muzzleloaders--- especially if something went wrong and you get slow ignition or a bit of a hangfire.
I once used my 22 rimfires for this kind of training, but that meant a trip to the range and sometimes long waits between sessions.
In recent years I've switched to pellet rifles, which allows me to shoot at home. I thought I would throw up the topic and see if anyone else has resorted to the same tactic for their "muzzleloader" practice. I have to say that firing 20 pellets a night, every night, has done more for my marksmanship than shooting many pounds of black powder.
While any pellet rifle will help and I've made do with some really cheap ones, I recently splurged and got a Beeman R-7 with a Bushnell air rifle scope. The whole package set me back a little over five bills, but man, is it worth every cent! It is so accurate that if I miss, even by a little, I can be certain that it is entirely my fault and not the gun. This little wonder easily stays inside 1/4-inch groups at 50 feet with cheap standard pellets. You don't even want to know what it will do with those expensive match pellets.
Advantages of the R-7 (850 fps) are that it's quiet compared to the 1000 fps "magnum" versions; lots more accurate; lets me use a cheaper scope; and requires 18 pounds of cocking effort compared to over 40 pounds for most other magnums.
Results of offhand practice are so good for my muzzleloading that my long time shooting pardner commented on a recent shoot. "Are you using a new load or what? You never miss!" I was centering the 6" bull shot after shot at 50 yards and he was doing good to keep all his shots in the black. After shooting my R-7 he plunked down five bills for his own, so watch yourself out there!