I am building a scaled down replica of a civil war cannon and need help with the design, bore size, wall thickness, safety factor, etc. I am melting copper, tin, and zinc to make gunmetal (88% copper, 9% tin, 3% zinc) and casting the barrel. Doing it the old fashioned way! My size is limited by the capacity of my crucible which dictates about a 3.75" breech diameter tapering down to the muzzle. Minimum dimension is around 2.75" diameter, barrel length about 22". I was planning on drilling a 1" bore, which would leave me 1.375 wall thickness at the breech, and .875 minimum wall thickness. I've done a test pour and tensile strength tested the resulting metal which broke at 20,500 psi. I would use only black powder which has a max pressure of 27k psi. I'm not an engineer, so I have very little knowledge on how to calculate the strength of this barrel with the above parameters. I found a hoop stress calculator which is typically used for static pressure in cylinders (https://www.easycalculation.com/physics/classical-physics/stress-circumferential-direction.php) and according to it the stress goes down below 20k psi just 3mm into the wall from the internal bore. Stress at the outside of the barrel is only 3800psi, well below my 20,500 breaking point. While this seems reasonable to a layman, I'd like to get input from somebody who really knows how to figure this out. Let me also mention that I know this is not a "safe" cannon. 10% of historic cannons blew up injuring their operators. I never plan to fire this cannon without strict safety measures. Meaning, light the fuse and get behind a significant barricade that will protect me in case of failure. I may also use a remote triggering device. I never plan to fire this cannon with people standing in the open where someone could get hit with shrapnel in case of failure.