Shifty-
I turned the barrels on a wood lathe. Wear saftey goggles!
Once you get the barrels turned pretty close to size, then use sand paper to finish. Use a rougher grit then slowly step down to a fine grit. I learned by just reading on custom calls. My cousin and I came up with a jig for the insert, but we've yet to test it.
He has all the tools and he lives 2 hours away so it is not too often we get to play around in the shop together. I'd start with some cheap wood for practice before you buy the good stuff.
Hutproducts.com is another good source of materials. We've turned out of oak, redoak, blackjack, pine, and black walnut. All are really cool, but the sound (important part) comes from the insert.