I bought my round ball mold from---
http://www.jt-bullet-moulds.co.uk/Excellent quality.
Also, it seems to me that this therad was all about round balls in smooth bore "shotguns", not muzzle loaders or rifled barrels.
The philosophy to accurately shoot round balls from smooth bore, as far as I have been schooled, basically breaks down into TWO approaches.
One---Size the roundball to the internal bore diameter and yes this would mean the choke, or in my case cylinder/cylinder bores.
Two---Use a smaller diameter ball WITH a carrier to keep the round ball centered (aswaged) through the bore---a favored method is a shot cup with the petals cut off and placed upside down in the hull to HOLD the round ball in the laoded 12 gauge hull. The shot cup is what rides on the internal walls of the bore during its flight up the barrel.
I use a combination. In part because I think the inverted shotcup eliminates potential for blow-by since no molded round ball is as perfect as the bore diameter. However the round ball mold I had Tanner make for me produces round balls that essentially match my .724 bores.
Wheel weights or a trace of a % of alloy to harden the lead should not damage the bores. I also bake the round balls and cool to harden them. No damage to the bores. But definitely harder and in my opinion stronger than pure lead... Sure, if you put too much alloy then the round balls are very hard and they could damage the bores, but if you add too much alloy they will also be very light in weight... so you can measure if you added too much alloy if you weigh the round balls and they are much lighter in weight than the same sized round ball made from pure lead. I do not like pure lead because it is too soft and breaks up too much in my humble opinion, and even against deer I prefer harder than pure lead... although 99% of the deer you shoot where you should be aiming for with a pure lead round ball is a dead deer. But since I plan to hunt hogs and big cats then a hardened lead ball is superior to soft lead for all seasons, so to speak. ...I learned first hand about the too light problem when a friend said he had perfect lead for round balls but I weighed them after we cast up a few. They should have weighed in the 700 grain range instead they weighed an astonishing 560 grains.... needless to say I did not shoot them.... but they were very, very hard. WE also stopped molding any more of those ultra hard, ultra light "marbles".
I would think the off-the-shelf .690 round ball or my preference a .715 round ball would work very well in most 12 gauges that are anything bigger than a full choke IF you use the carrier approach. Bear in mind: the off-the-shelf round balls are pure lead, hence soft, so they should pass through a choked shotgun without any issues.
I think there is something aesthetically appealing about the round ball especially in a double. And since most shots in the East for deer or hogs or cats is under 50 yards, then the round ball---when made to shoot accurately and tested for performance--- can be lethal as well as a thing of beauty.
