 Design work may have started before the First World War, however the company gave precedence to military requirements so work on the compact 6.35 mm only resumed at the end of the conflict.The first version of the gun was very similar to the Model 1922; nearly a scale model in fact, with the single important difference of a spring-loaded firing pin rather than an internal hammer.Mechanically this change was detrimental; it was probably made due to considerations of size.