…25 March 1991 Talk with Doug Brassard S&W Customer Service
SAAMMI allows a rear diameter of .4862 nominal plus .004 and .4806 plus .004 for front of the 45 Colt chamber. When I asked him about the 45 Colt ball chamber throat diameters he said that they used to be .4545 to .4565 but now they were .452 . Smith and Wesson has its own standards for the barrel dimensions for the 45 Colt and they are : one turn in 20, 5 groove, lands .444 -0.0 + .0012, groove .451 - 0.0 + .0017. For the 45 ACP it is a 6 groove barrel, 1 turn in 15 inches, lands of .443 -0.0 +.0012 and grooves of .450 -0.0 and +.0017. Interestingly enough the SAAMMI specifications for 45 ACP lead bullets and jacketed bullets are different. Jacketed specs are .452 -.003 and lead bullets .453 -.003.