As long as bore and twist match the desired caliber it's no biggie. My buddy Mike Bellm cuts the cleanest most precise chamber in the business bar none. I spent some time with him trying to learn his method but it would take more time than I had. Right now I've just re chambered a 15" 45-70 Encore barrel to 458 Lott which will also allow the use of 458 Win Mag ammo. Because the 45-70 twist is designed for lighter bullets I usually run 350gr Hornady RNSP bullets but accuracy with 500gr solids was acceptable. I have a 24" 45-70 barrel on the way that I am going to cut back and chamber in 450 Nitro Express and for it I am loading 450gr Swift A-Frames. The other project going at the moment is an experiment. Since TC doesn't make a factory .511 barrel I have a 15" 500S&W barrel with the muzzle tamer coming and I am going to chamber it in a modified 500 Nitro Express. My initial loads will be with .500, 500gr Hornady XTP's but I am already working on a proprietary hard cast design through Mountain Molds in the 550gr to 600gr range. The largest I've done in the past were the Lott's. That is the only time a handgun has set me back enough to have to take a step backwards so the Nitros should be interesting although they are lower pressure loads.

I won't be wronged. I won't be insulted. I won't be laid a-hand on. I don't do these things to other people, and I require the same from them. John Wayne-The Shootist