Originally Posted by
Semisane
OldBob, there's no way the base of a ball can be flattened inside the barrel, unless perhaps there's a wad between the powder and ball, or the ball was pounded mighty hard against the powder charge in the loading process. With nothing between the ball and the powder pressure is equal on all parts of the sphere exposed to the charge.
Semisane,
You hit the nail on the head. I should have been more explicit. I was working with cartridge shotguns, and I was using a wad, and a hard one at that. Accuracy was all about wad selection. Softer wads, like the Winchesters, deformed, and the accuracy was erratic. At one point I contemplated using a .135 card wad to support the wad floor, but I never did. Lazy slug that I am, I just went to using the harder Federal wads. I was getting 2-2 1/2 inch groups at 50 yards out of a smoothbore, so I stopped there. Intended use would be similar to crossbow range, 50 yards max.
Interestingly, I had the same experience out of a TC Black Diamond with Buffalo Bullets sabots. The bullet was pure lead, and had a nice boattail shape. Accuracy was decent, bullet expansion in newspapers looked good, but the nice boattail turned into a bevel base. The only place that could have happened was while it was inside the barrel. The loads weren't heavy, either, since the plunger-style bolt would blow back and crup up the underside of the scope.
My guess is that pressure IS equal on all parts of the base, but that the pressure cause the bullet to compress lengthwise, increasing pressure. I think the best solution is to use a flat-based bullet of stronger construction, and alter the nose to cause expansion.
OldBob