i know the rifled barrel is designed for sabots but is there anyone using the cheapo lead rifled slugs in there rifled barrels?. i have tried it in the past with a 12 guage with good results but is this bad for the barrel other than lead build up?

No harm to the barrel. Reason its never suggested is because you'll likely waste all the $$$$ you spent on the barrel.

Still don't know why they haven't come out with a .730 ball (like a muzzleloader) slug. That way we could have a cheap alternative for our rifled barrels.

It will not harm it, but it isn't very fun to clean. My slug gun will shoot rifled slugs pretty accurately if I choose the right ones, but only for about 4 shots then the barrel fouls out. It will fill the grooves with lead and start to effect accuracy. Then you have to clean the barrel, which will be a chore compared to shooting sabots.

Not to mention the newer sabot ammo has better ballistics and better designed bullets.

Paul