NO, YOU ARE NOT !!! Also, you CANNOT measure the muzzle as you have done and expect anything approaching the correct ID as you are measuring the lands that way NOT the grooves.
In my three COLT pistols, the S&W 44-40, and the two CIMARRON 44-40 pistols all will shoot just fine with .428", .429" and .430" [ you can run into chambering problems with this bullet OD..] OD bullets. I might add the CIMARRON '73 44-40 does the same.