Actually, I havent yet miked it, just was surprised one day when having the cylinder out, I tried putting a bullet in the wrong way just to see how tight it left the chamber and was very surprised to see it didnt fit, I tried factory and home cast sized .429 and no way, which made me think for one the pressure level must be higher than normal in the cylinder as it wants to leave, and second, the bullets are resized aprox. .428 before entering the barrel!