>interested in mounting it and firing it on holidays, etc.
I don't recommend firing salutes from this gun, using black powder. Current practice is to leave old cast iron guns on display and not shoot them even with light loads of black powder. If they must shoot it, please investigate rigging it up with a propane/oxygen/electric mechanism as many reenactors do now to simulate artillery fire. The cost is much lower and it is much safer than black powder.
The only even marginally safe way to shoot it with black powder would require boring it out smooth, then fully sleeving the bore with a cemented-in 3/8-inch thick seamless steel tube, closed at the breech by sweated plug, with certain machining radius required, etc. etc. per NSSA rules. That modification would run into the thousands of dollars. Even then, the bore is really too long for firing salutes and safely servicing the piece since this will be done by untrained amateurs on a very infrequent basis.
Historically, the most accident-prone cannons are original "town square" cannons fired on holidays by well-meaning but improperly trained and equipped people. Many serious injuries and deaths have occurred in these incidents. When I worked for the Navy I assembeled a long list of gruesome muzzle-loading cannon accidents that had been reported in the press around the United States.
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