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topic 10739

Need information on the internal bore of a black powder cannon



I am currently constructing a black powder cannon and have managed to get everything perfect except for the internal bore. Due to the vibrations involved when using a boring bar on a metal lathe there are little grooves all along the internal bore. Is it important to have a perfectly smooth bore, due to the grooves is it likely to explode? The cannon is made of 64 mm diameter mild steel and the bore is 1 inch in diameter, it would be greatly appreciated if any one could give me any relative information on this subject or could tell me a method of smoothing internal bores, not to difficult though.

Thank you,

James Munday
- Tasmainia, Hobart, Australia


You can smooth the bore with a flap wheel sander or slower, but better, use a hone. Get about three different grades of abrasive sizes or it will be terribly slow. Option is to start with the coarsest one you can find. If the finish is fine after that, quit. If not, go to a finer stone.

James Watts
- Navarre, Florida


The grooves won't endanger anything.

If you still want the interior perfectly smooth, go to an auto parts store and ask for a brake cylinder hone. The gadget will usually have 3 or 4 spring-loaded arms with a polishing stone at the ends. Run this up and down your bore with an electric drill a few times to take the grooves out.

64 mm OD and 1 inch ID is safe enough for salutes and very light projectiles like wood targeting balls. Anything heavier, consult a serious black powder outfit. Pyrodex in particular can tell you all about safe pressures.

Dave Fitz
- Ogallala, Nebraska, USA


Cannon builder: don't think the grooves will hurt a thing, but if you want a smooth bore then you might want to use a 1 inch or a 1 1/16th ream. a hone will also do the job as the other two responses noted. Got any pics of that jewel?

Mark Jackson
- Charleston, West Virginia

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