"Do-it" brand "cannon ball" sinker molds work reasonably well, and are fairly cheap.
The 4 cavity 1, 2, 3, 4 ounce mold goes for $39 bucks retail.
The 3 ounce sinker has worked well for me in my 1" Brookes Naval and Dictator bores (.96 diameter ball). It is not a super high precision ball, but "adequate" for casual shooting. For instance, it will have the weight on ounces cast into the ball.