The MK-V was designed to lower Colt's costs. The finish and machining were not near as nice, and I believe it was the first Colt to come with rubber grips instead of wood. They were made in 4 & 6" barrels, but I never saw a 4". I had a MK III and a Python, while a buddy of mine had the MK V; you could REALLY tell the difference when shooting! While most all of Colt's revolvers shared the same lock work, the later models were not nearly as polished. It was a sad decline to watch.