Just my two cents...
Fwiw, I have made a bunch of wooden ones. Some I kept, others I gave as gifts. Never had any swell, but then I live in a dry state, humidity wise. Made 'em out of maple. Now, the way I do it is to use a standard adjustabe powder measure, find a drill bit that just fits the inside diameter of it and measure the depth. A drill press is almost a necessity for accuracy. Sure, you have to play around a bit, but once you get the hang of it, it is fairly simple. The outside you can make almost any shape you desire. Are they historically accurate? I have no idea...but it works for me. Re using brass...I doubt if any of the old trappers in the Rocky Mtn's. used brass...where would they get it from...and if the did get some..if they lost it...either antler or wood is my guess.