True that.... I picked up a cap and ball .36 Navy revolver replica that shot pretty well. No paper work and no permit required due to it being a black powder gun. Not too accurate at any distance but tons of fun for making noise and busting melons and paint cans relatively close up. I have since retired it to paperweight status. It still works and shoots but I have decided not to shoot it again. The metal is not tempered and therefore the weapon is not safe.
That CO2 cylinder packed with match heads would likely have exploded rather than launch as you were hoping for.
I've made one of the drink can canons with duct tape and cans. Lighter fluid and a flame..... BOOM... sounds good.
At a bluegrass event I attended on a annual basis years back, some of the guys had made a number of potato cannons. PVC pipe, some fittings, and a BBQ grill igniter and some white rain hairspray and a bag of potatoes.... we were launching from the far end of the campground, over the heads of the crowd, and targeting the cows up on the hillside on the other side of the creek. Cows were not hit by any of the spuds.....Those cannons were really well made and had a nice range. They brought about 10 of them and sold them to anyone who wanted to join the fun.
You can find all sorts of idiocy on Youtube involving homemade guns.
There are always idiots when it comes to guns and safety. But to infer that criminals are safer with their weapons than the average citizen is totally ludicrous. These are the same kind of people who, if handed a sword, would start swinging it around in their living room and as a result, smash and slash the lights, ceiling fan, and couch cushions since they have no clue on proper swordsmanship. The idiots who mishandle their weapons and cause an accident, are, I believe, a very small percentage of non-criminal gun owners. We tend to hear about their misdeeds due to the entertainment value and the agenda of the media which is (generally) anti-gun. You rarely, if ever, hear about the safe use of guns, and the many times every day where a citizen uses a gun for self defense to prevent a crime and never pulls the trigger. Most of the accidental discharges are due to that person ignoring the safety procedures that every gun owner has a responsibility to know and practice. Firing a rifle or a pistol into the air is the height of irresponsibility and I am 100% in favor of charging them with a crime and the results of the consequences of where that bullet goes and does. A number of states already have laws against shooting into the air. Shotguns with bird shot are in a slightly different category from rifles and pistols.