Still trying to chrony my small burst disk hybrid. Set up everything in my yard today (as my preferred shooting location was occupied) and since I was shooting a 10mm ball bearing I went overkill with the back stop and got a 20kg bag of dirt, two local phone books and filled a 70cm x 30cm x 30cm polystyrene box with water. Just before I was about to shoot, I pussied out
After all that, I still couldn't be sure that the ball bearing would pass through the chrony and the backstops without deviating and ricocheting of nearby concrete walls. My house was also directly behind me and it has a lot of large glass doors on the front.
It wasn't a complete lost though, I had scored the four soda can burst disks with an X beforehand and when I pussied out as detailed above, I shook the barrel to remove the projectile and then fired the cannon in to the ground. I got a lovely burst on every disk and all the pieces stayed attached to the disk which is handy for when you don't want to shoot burst disk at your target or have them cut up a sabot.
Edit: Oh and it was f*cking loud for a shot with a barrel. Perhaps it was something to do with the acoustics of firing in to the ground in my yard as I could hear it resonate throughout the neighbourhood as more of an explosion than a firearm-like sound.