Thanks for the interest. I will take some photos of the barrel-making process and capture my screw-ups, failures, and triumphs. But then, I will need help with how to post them. Computers and me don't mix.
Trunnion Lathes, etc.
I don't know how large a diameter barrel that you are going to machine, but (I'm speculating), making a barrel with intergral trunnions will require an incredible amount of machining, and stock removal. Also, how will you machine the band of remaining metal from between the trunnions? You could turn the profile of the barrel from muzzle to breech, except for the area surrounding the trunnions, which will still be at full diameter across the trunnions. Even if you found a way to machine the trunnions (milling machine, w/boring head, etc.), and remove the band of extra metal, you will still need to hand file and then finish the area around the rimbase of the trunnions, to blend them into the curved and tapered, barrel. (I'm envisioning a traditional cannon, i.e. a barrel that is tapered from breech to muzzle).
I suppose you could remove that problematic, band of extra metal from between the trunnions, by doing some kind of a set-up in a milling machine so that the barrel could be slowly rotated under a cutter, and by degrees cutting away the metal to match the taper at that section of the barrel. You might even be able to machine away that band by using the lathe carriage and a cutting tool, as a "shaper", while the barrel is mounted, and rotated while still chucked in the lathe. I'm no machinist, so maybe others will come up with alternative, and more efficient ways to machine away all this extra metal. My guess would be that the whole process is quite a huge p.i.t.a. One bad cut, and oops!
Honestly, I don't think there is any "easy" way to machine integral trunnions. Most modern reproduction cannons made from bar-stock, have trunnions welded onto the tubes....unless of course, the finished cannon barrel started as a casting.
Judging from the old engravings that I've seen, I believe that "trunnion lathes" were mounted at 90 degrees to the length of the barrel and came in with some kind of cutting tools to machine the circumference of the trunnions while the barrel was still mounted in the lathe....but the extra metal must still be machined from between the trunnions. But how? I have no clue.
Go for it... Make a barrel. We only live once.
EDIT: Go to: "Seacoast Artillery" for photo of a cannon barrel being machined in the area of the trunnions.