Yes, You're right, using some heavier denser metals would be better, such as lead. I was trying altar one of these balls slightly, so it was different from the other solid stainless steel balls. Had some 3/8" diameter brass on hand, And its color is different than the stainless. Therefore, I could see this ball is different than the others.

I'll definitely get to some lead, think I might have to melt it and pour it into the ball. Or try a solid lead ball, but lead is pretty soft so it might get beat up Pretty good going down the track.