You have a lathe, right? I don't know how you could do it without one.
Alignment is the hard part. Aligning the tailstock so that it is not out of round, aligning the barrel in the headstock, ensuring the barrel is thin enough to fit the headstock, etc.
Its a pain to set up, then you just "ream it out"!!! The reaming process is slow, and you use something like motor oil to lube the cutter. Use a "roughing reamer" for most of the cutting, then a "finishing reamer" for the finishing cuts. Or just use a finishing reamer - slowly - for the whole thing.
Look at the Reamer Rentals .com website - they explain how to use their reamers and that's pretty much it.