The traditional forms of celebration of the founding of a country of free men having been largely forbidden by the government, it is left to us to figure out how to accomplish this with the available resources.
This is a model of a Dahlgren-style black powder cannon of the sort one might find in the late 1800s. This particular item has a bore of 3/4" which opens up several possibilities for loadings.
This is fired with a fuse, which allows for retreat to a safe distance when firing. The originals were fired with a quick match, which was similar in function, but faster. That much detail was more than I wanted to get in to.
The wedge under the barrel is the usual procedure for elevating the barrel. Presumably the operators would have worked out the ranges at different elevations, and marked them on the base plate under the wedge.
For general noise making, about 30g of 2 or 3f black powder under a wad made of 3/4" Ethafoam will certainly do the job, and with a minimal recoil. The bore being what it is, shot cups from a 12 ga will fit smoothly down the barrel, and at an extreme, a 1 oz 12 ga shotgun slug could be loaded in to it.
The gun weighs 13 lbs which is heavy for a 12 ga deer gun, but think about the expected recoil. I would not fire this with a heavy projectile without coming up with a way to anchor the gun to whatever platform it was shooting from, preferrably with some elasticity involved to avoid sudden impact. Cannon from this era were normally loaded with powder never greater than 10% of the projectile weight. For something untried, I would start at 5% or less, which works out to about 20 grains. Note also that the cannon wall thickness is approximately equal to the bore of the gun. This is a good starting point.
It's not really done yet. Before shooting any heavy loads, I intend to cut the top of the carriage, and add Iron straps to hold down the barrel, this should result in greater historical accuracy, and a much diminished likelihood of the wood splitting and the barrel flying back into someones vehicle. The wood is Maple. Use only hardwood.
WARNING! CAUTION! DISCLAIMER!
This gun was machined from a solid billet of good grade steel. Putting powder into a piece of pipe, no matter how good it looks, is a bad idea. Before you rush out and build a historically accurate replica of the guns used at Ft. Sumner, only to find you have built a historically accurate pipe bomb, consult with an engineer with some experience at calculating the required size and strength of large hydraulic cylinders.
If you don't know what the math is, or can't do it yourself, I would strongly suggest not doing this at all, or at least farm it out to someone who does, like Dixie Gun Works.
Happy 4th of July.