The Can Cannon by X Products definitely falls in the latter category. It's a modified AR-15 upper which attaches to any AR-15 lower and enables you to shoot 12 oz soda cans. .223 caliber blanks can propel the cans way beyond 100 yards and it's a really fun product.
In this video I was at an event where the Can Cannon was present so I only had a few minutes with it. However, I have one on the way so I will be shooting more things out of it soon!