Folks who know me know that I am very particular about which rifles are fed "J" boolits and which are only fired with cast boolits. Any Winchester levers, Martini's, Sharps and several classic bolt actions are only fed cast.
The cheapness of cast boolit loads means that I can afford to shoot much more than if I was relying on store bought boolits. Shooting more may mean that the barrel would be worn out quickly but I haven't seen that.
The payback is absolutely polished barrels that only get better with time. But the burning question that I am often asked is what barrel life can be expected? I simply don't know and don't have a clue. A Google search is even more confusing with 'estimates' running from 40,000 to 250,000?
I have new rifles and some old ones where changing the cast boolit size has made a rifle with useable accuracy. This is something you can't do with "J" boolits.
Tight Grouping from a 7x57Mauser
My Favourite - 30.06 Springfield.