You might also want the taper per inch from the 275 barrels in question. Starting with the muzzle OD and then measuring the OD of the barrel 12" from the muzzle then divide by 12. Do the original Rigby barrels taper .006 per inch ?, .010 ? or are they straight ? I think this info would be helpful to you . Our barrels taper .012 or .006 per side for every inch form the muzzle to the transition of the parabola just ahead the shank. This taper is not very common among barrel makers as .006 to.008 seems to be the norm.