Check the paint to see how it actually fits in the barrel and if its actually consistently round. Then do a drop test on a hard surface to see how brittle the paint is. That will give you an idea if the paint is brittle or not.
A large bore typically won't cause breaks but if the hopper causes more than one ball to enter the breach due to the detents not working properly, then it can become a problem. Metal nubbins should be fine. The only reason plastic ones are better is because they don't break and get caught in the bolt mechanism and scratch things up inside the barrel. Wrap a piece of tape around the barrel where the little knob is located at the back of the nubbin if it is a plastic nubbin. That will push the nubbin farther into the barrel. If its a metal one, put a slight bend in it to do the same thing. It might help.
Except for the Automag in front, its usually the man behind the equipment that counts.