I recently bought a 686 and was wondering what it means when people refer to them as a 686-1,686-2 ,etc;Mine is just a 686 so is it an older model ??.Phoned S & W 1-800 number and they said from my ser # mine was made in august 1986.
In Engineering speak the dash number denotes an engineering change to the assembly. If they change a scew length or thread or a machining process or make any change so that it would be different from the basic part, they issue an Engineering Order (commonly called an EO). That EO shows the change to the basic drawing and changes the part of the drawing that identifies it. They sequentialy increase the dash number with each EO. EO's are directions on how to change the drawing so that a variation of the basic part is documented and can be made. At some point the actual drawing is changed to incorporate all the EO's which includes identifying the part with the last issued dash number.
In short each dash number represents that a change has taken place to the original basic gun assembly. As it turns out some dash number add very little to the guns and others are major changes. There is no way of telling without reviewing the drawings or summaries of what each dash numbered change did.