I would have a gunsmith/machinist with a lathe do this for you...
Dave is correct, thats allot of difference... Maxi/Mag, 455/44M, 454/45Colt are allot different. These three are easily done by hand. With a 220 its larger in diameter over its full length... IMPOSSIBLE to get and keep straight by hand. I did a couple 17HH from 17HMR barrels, I used my drill press with a centering quill. (NO power, just to keep things straight) I still screwed up one chamber...
Its a nice caliber, (I would go 225 myself) but don't waste a good barrel, a GS shouldn't be more than 100 (and thats steep).
CW