When hunting, bouncing around the countryside with large diameter, low sectional density projectiles is a moot point, imho. Their range is VERY subdued. Steel balls would be very poor hunting projectiles except at very close ranges with large bores. Small bores, ie: 24 gauge would probably only work well on deer or other 'light' game.
The point is, with smoothbores, protecting the bore is easily accomplished with a descent patch - rifles are a different story. The fit must be tight enough to spin the ball and lubricate as well as soften fouling. They also have cornered lands that might be susecptable to damage from the hard ball due to cut patches, the ball being forced against the cut-side by the other's press fit against opposite lands. That ball, exiting at velocity has the potential to ruin your barrel. The material used must be soft enough not to damage. The ITX ball I centrepunched with a sharp pointed punch, was barely marked and the mark could barely be seen - mostly only felt with a finger (someone else's - mine are a bit toughed for fine observation. It is possible the ones I received were harder than normal - I don't know - the possibility of those to do damage was not only a possibility - the one I pushed through the bore did in fact mark a land (press/score) and created flattened areas on 2 of the 'belt's' corners when the ball was loaded with the belt running vertically. It tilted as it was pushed down the bore - which was a major chore, btw. If it was difficult for my ham fists - as well as for Pletch and Steve - those who like to thumb start will have to learn to put some muscle into loading these as presently made - or simple go without anything more than .005" and wipe between shots.
Fact remains I would most heartedly endorse the 'project.product' if the balls were made smaller and in a size I could test. I have available for testing, .45, .40, .32, .58 and .69 cal rifles as well as a .62 smoothbore. For the smoothbore, the ball should be .595" at the most, and possibly best at about .585" to .590". A .675" ball (15 bore) would work well in the .69, with .560" for the .58's, .435 largest for the .45. A .50 ITX should, in my line of thinking, be about .490" largest - ie; band corner to band corner, instead of .503" and .505" as measured by me.
All measurements I've made are the largest size of the band to allow the bands to be unde bore size, corner to corner. Having them larger than the bore is an invitation to trouble, I believe. I've been proved wrong many times, btw - just my gut feeling on size being spoken here.