Currently building my version of a Naval 24 Pounder. Barrel is 1 5/8" Dia X 9 5/8" length with a .500 bore. Barrel started it's life as a piece of 1 5/8 hex brass which
made it easier for me to locate and mill the trunnion pockets on my small mill.
First step was turning a few diameters for the steadyrest to ride on then centering, drilling and reaming the bore. Then on to the mill for the trunnion pockets then the turning can begin.
Joe