On Mackinac Island at Fort Mackinac the boyscout honor guard uses one of those WRACO cannons to fire a shot just before the bugle call for morning and evening flags every day, all summer. The first cannon they had served from I would guess the 1940's to about 2001, when the pin that the breech block hinges on fell out. The identical replacement is now in service.
The elevation screw is really like a limiter screw. When you pull the lanyard the hammer snaps forward, and the pull from the lanyard points the muzzle at the dirt. All the screw does is limit how high the muzzle can go, I think it's just there for looks. The 10 gauge blanks we use are louder than the quarter-size saluting charge the fort soldiers fire from their 6 pounders! They work well for making noise, but I wouldn't try to fire a slug from one or anything like that.