The barrel on this rifle was from a .50 BMG and has a twist rate of one turn in 15 inches. I think that is way faster than needed to stabilize the lead bullets I am using, so is probably not ideal for accuracy. Plus the bullets may be slipping in the rifling because the pitch is so steep. However, the rifling is very deep which may be good. And I don't think the barrel is super-smooth either. Anyway, I think this rifle may not have a lot of potential for accuracy compared to one with a barrel better suited to a black powder cartridge. Here are some photos to show some groups.
Above is a group at 50 yards with 600-grain Barnes Originals, their old soft point jacketed bullets. Power charge was 115 grains of AA8700 and velocity was 1,600 fps. It's the typical 4-MOA group I would expect with that load, but I was concerned about pressure because the barrel's groove diameter is 0.507 and the bullets are 0.510. That's what got me started into paper patching.
Above is a group with 720-grain round-nose paper patched bullets. The bullets were cast from an NEI mold I have, which turned out to be too large in diameter, (my mistake). I had them lathe turned to a smaller diameter. The powder charge was 115 grains of AA8700. The same as for the 600-grain Barnes bullets, and the velocity was 1,750 fps. That's 150 fps higher with a heavier bullet. The folks at Accurate Arms told me the reason is because their AA8700 powder is not burning well with the light 600 grain bullets. That is, the heavier bullets let the chamber build up more pressure for a better burn. This was a 50-yard group, again, about 4 MOA.
Above is a 5-shot 100-yard group of about 2.5 MOA. This was with 690-grain round-nose hammer-swaged paper-patched bullets. Velocity was 1,660 fps and the powder charge was 110 grains of AA8700. If it shot that well all the time I would be happy as the smallest animals I will probably shoot with it will be whitetail deer, and that's good enough accuracy to get them at 200 yards. And I think trajectory limits this rifle to around 200 yards.
Above is a 100-yard group of about 2.25 MOA. This was with 575-grain hollow-point hammer-swaged paper-patched bullets. Velocity was 1,625 fps and like the group above it, the powder charge was 110 grains of AA8700. Again reducing the bullet weight resulted in a lower velocity. Again, I think groups like this are fine for this type rifle.
The above group is the same load as the previous one except that the bullets weighed about 580 grains instead of 575 grains. However, accuracy was poor. This is a 50-yard group so it is almost 6 MOA. The only thing I can think of is that the more accurate groups were shot in cool or cold weather. This 50-yard group was shot during August when the temperature may have been 90 degrees F. I had a .22 Hornet that shot under 1.0 MOA during hot weather, but about 2.0 MOA during cold weather. Maybe this rifle and loads behaves in just the opposite manner. I will try it again in a month or so when we get cool temperatures.
The above photo is of a 575-grain hollow-point paper-patched bullet I dug out of the dirt behind a 100-yard target. This was a hot load with AA3100 powder with a muzzle velocity of 1,900 fps. They say one needs to use pure or at least a very soft lead for hammer-swaging. However, I think very soft lead may expand too much at 1,900 fps for use against large game where good penatration is required. Notice how the bullet is almost turned inside out. That is a .380 pistol cartridge inside the back-side of the bullet. If I would ever use this rifle on large game, I would cast bullets out of a harder alloy and lathe-turn them to proper diameter with large flat noses, and then I would paper-patch them.