That looks like a lot of work to make a 12 ga. slug that won’t be as effective as a lead slug. I liked the music though. lol
Slugs are hard to come by and expensive, more than a dollar a round. Bird shot is widely available and cheap. Look into the waxer a little deeper you may find that there is a reason your assertion may not be right. There is a physical reason the waxer distributes force differently than a slug. Some people use hot glue or just wood glue, but wax is much cheaper.