I have never had any Ball-etts, but there is something that sounds similiar. Hornady makes a 50 cal. 240 gr. PA conical. Having a .512 front band, they do not require a patch and shoot well in my traditional Investarm. They are concave on the back, I suspect that the skirt expands and grips the rifling. They are heavily lubed. I don't remember what they cost, I got them at MidwayUSA, 50 in a box.