I have been casting round balls and conicals for years(many years) with straight WW and with pure lead. I have never been able to tell a dimes worth of difference between the two in accuracy. I have noticed I have better retained mass with WW.
I believe the harder lead was a bit of a problem in some of the old soft steel barrels. But I only shoot modern barreled MZ's. And with a round ball that would not matter. It would only matter in a conical. Round balls will work perfectly.
Some people say WW will not expand. But that is simply not true. Pure lead round balls do not "expand" either. A properly expanding bullet does not shed any of its material. The proper term is a "mushroom" of the bullet. And WW will "mushroom" very well, and it will retain more weight than a straight lead round ball. Which will in the end yield more penetration if you need penetration.
What a round ball does on impact is what limits their range. A pure lead round ball sheds its mass quickly for less retained weight. That is a problem-not a good thing.
And as far as a tight fit is concerned?? Well we all use patches with a round ball. So you adjust your patch size with WW the same way you adjust your patch size with pure lead balls. You have three variables in a MZ when shoting round balls. That is the ball, the patch, and the internal dimension of the barrel. In order to accurately shoot an MZ you need to sometimes adjust these dimensions. And the easiest one to adjust is the patch. So you need to adjust patches with pure lead as well as you need to adjust with WW. And the real size difference is almost immeasurable. Tom.
wheel weights?
