 Schofield's improvement called for heat treated, replaceable components at this sensitive "wear" area of the catch and latch.The serial number range also will give an indication of whether it is First or Second Model, with the serial numbers changing from the First Model to the Second Model at a little over 3,000.In 1877, S&W discontinued production of its other Model 3s such as the American, Russian, and Schofield—in favor a new improved design called the New Model Number Three.