Same magazine body, but different magazine butt plate when the original 3913TSW was being produced. The original TSW butt plate was wider and flatter, and was intended to fit the cutout at the bottom of the grip frame, making the magazine fit flush to the grip frame of the early TSW, on the sides as well as the bottom.

Here are some thumbnails of the standard curved butt plate on a CS9 magazine and an original 3913TSW butt plate on another magazine in the same gun. The TSW butt plate is the wide, flat one. In the image of the butt plates by themselves, the standard curved one is on the left and the TSW is on the right.







I have a friend who bought one of each CS9 & an original 3913TSW when they were first released. He preferred the curved butt plates on the magazines (for his little finger), and didn't care if the sides of the grips stick out over the butt plates a little, so I installed curved ones on all of his magazines and he used them interchangeably in both guns.

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Ret LE Firearms inst & armorer