Scott- you can easily use alloyed lead for shooting, however the ball diameter becomes critical. You will not be able to load as large a hardened round ball
as pure lead, with a given patch, as the lead and patch will not conform to the bore as easily. This means that if you reduce the size of the harder ball,
you might still be able to load it and get good accuracy.
In theory, the smaller ball will not give as good accuracy as the larger, softer lead ball. If it did, then the Bench Rest shooters would be using smaller, harder lead balls
for competition shooting.They do not. They use bore size or over bore sized round ball AND .020" to .022" teflon-coated patches.
Due to my desire to shoot harder balls, particularly for hunting, I had the late Jeff Tanner, make me a 15 bore ball mould, ie: .677". It casts .677" balls of alloyed lead.
I load these quite easily in my .690" bore with .714" groove diameter using 13 and 14 ounce denim. I measure that denim with a mic, at .025" and .030", (adding .005
& .004" for caliper measurement, compressed. That mould casts pure lead at .675" and loading is very easy with the thick denim patches. Accuracy is the same.
The accuracy at 50 yards, is similar (virtually identical) to shooting pure lead balls of .682" with the same thick denim patches. In this case, the harder, but smaller ball
was able to be loaded with the same patch, as the 005" larger but pure lead balls & with the same patches.