I am not an authority on cannons but seamed tubing is generally not considered as strong as seamless or DOM (drawn over mandrel). I have never personally seen any split in a wreck, but many race associations will not allow seamed tubing in a roll cage. The seam projects inward a little so it would keep your projectile from being centered.
It's the old Damascus steel theory. Welds make micropores. Pores attract blackpowder fouling. Black powder fouling is hydroscopic, it attracts moisture. Moisture and black powder fouling cause corrosion/rust.
Corrosion/rust make pits. Pits attract black powder fouling.... you see where this is going.
I have seen old damascus shotgun barrels let go.
We had a black powder tennis ball launcher made of schedule something or another welded pipe. After we fired it we would rinse it out with a garden hose and let it dry. One day, after we fired it we noticed a hole in the side about the size of a nickle. We never heard it or saw it go. Hole was in the direction of the shop. Never saw a mark any where. The crack that ran from the hole had rust in it.
Rigth after that i started to find out how to make a proper cannon and built my first Beer can mortar.
Are you saying that the ball sticks part way down the bore, or that it sticks going down the bore.
If it sticks part way down the bore in the same place every time then you do indeed have a tight spot that needs reamed or honed.
If the ball sticks going down the bore the ball may not be round. Roll your balls...the cast lead ones...across a smooth flat floor. You will spot an out of round one real fast. Those flat cast aluminum fishing weight mould are notorious for being out of round.
When using Seamless tubing, chuck that tube up between centers in a lathe and true the out side. If one end is a bit off center use it for the muzzle end and it will center when you cut your taper.
Make sure you have an impact zone when you fire. Tell everyone it's for safety purposes. No one will argue you that. After everyone leaves go dig the fired shot out and reuse or recast. Don't tell your buddies.
Cannon sights are pretty simple to make. I had one of those cheap Italian Vernier sights that slipped over two pegs for a rear sight and a brass rod soldered in the top of the muzzle for a front sight on one of my guns. Got the idea at a cannon shoot up in Oregon. Several of the guns were set up that way.
You migh also visit this website for ideas. I think they have sights. http://www.cannon-mania.com/ Some of the other sites listed in the Black powder and cannon shooting resources note at the head of our forum might also have what you need.
Do you know if the casting was bored and then the liner inserted? Or was the casting made around the liner. My guess from the way you describe the problem, its the latter.
You are learning all the reasons why this is the wrong way to make a barrel. It sounds like the cast iron did not bond with the liner. Perhaps you have a air pocket around the bottom part of the tube or the upper part buckled during the pour.
When you drilled the fuse hole did you insert a fuse hole liner of steel or copper down the hole threaded into the liner. If not every time you fire the gun, fouling gets blasted into the seam between liner and cast iron. This can lead to rust and corrosion and a weak spot that can lead to an eventual blow out.
Because the chamber area is looser than the muzzle area, you have basically a constriction hazard. When you fire that gun the ball is flattened out to fit the chamber area. As the now chamber sized ball goes up the bore it suddenly meets the tighter bore constriction. The propelling powder gases look for an easier way out. The weakened fuse hole might be the course used by the gases resulting in a burst gun. This would not be good.
Fixes. I'm not sure it could be safely done. I don't know how the tube was made or why the constriction. I don't know if you have fuse liner. If you don't have a fuse liner, I don't know if there is any corrosion going on between the liner and casting. Do you know anybody who could xray the tube?
Maybe fixes. You could drill out the fuse hole over size and tap the hole and screw a threaded over size seamless fuse hole liner in place. You could hone the tight part of the bore out so that it is the same size or slightly larger than the chamber area.
If it were my gun, I would not do any of these things. I would render the tube inoperatable and NEVER fire it.
I guess you learn something new every day. I haven't inserted a liner in the fuse hole of my cannon and mortar since I bought them new last July.
Perhaps, Splendid Ha Ha could even use a slightly undersize ball to help eleviate any potentially dangerous situations concerning barrel obstruction. Or, perhaps you could just discontinue the use of a solid projectile and use lead buck shot, cast pistol balls, or bullets instead where the imperfect bore wouldn't be a big issue.
I personally enjoy shooting my cannon as a shotgun far more than shooting a single bore size projectile.
If the "shotgun" idea isn't appealing, you could always use it as a signal cannon only. However, if the tube was genuinely unserviceable or the owner had little confidence in the safe use of it, the choice would be better to render it unfireable.
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