I love this video, despite the dubious mini-cannon safety practices you see displayed here. The clip also reminds me that as a kid, I had a toy brass cannon that was a replica of a 15th century siege gun. It had a hole in the back for a nylon loop that connected to the spring plunger inside. Sometime during my junior high years I cut the loop and removed the plunger. I found that a Ladyfinger firecracker slid down the barrel perfectly, and the fuse poked out the hole in the end. The bore was just over .177 diameter so I could drop a BB down the muzzle. It shot the BB hard enough to embed it in basement sheetrock at a range of 10 feet.
That one shot convinced me that it wasn’t an inside gun, unlike this guy who shoots up the basement, the computer monitor and the vodka supply. Enjoy the video, but don’t try this at home.