A cool way to make a less then lethal round for your shotgun is:

Empty the shot out of your shell, by cutting the top of, opening it up. (BE CARFULL)

Fill the now empty load with silicon rubber, and wait for it to cure.

As I said BE CAREFULL this is not a safe round to shoot your buddies with! My brother uses them to move cattle. So a round of one of these may not kill but, it will put a serious hurting on you.