Originally, though, the small-framed hand ejectors were designed for...actually, developed hand-in-hand with...the .32 S&W Long cartridge. The .32 S&W Long wasn't actually all that long, unless you compared it with the original .32 S&W centerfire cartridge (now sometimes erroneously referred to as .32 S&W "Short".)
When Colt's released a snub-nosed version of their D-frame .38 Special revolver, the Detective Special, Smith originally responded with a 2"-barreled version of their .38 Regulation Police. Because these short-barreled .38 S&W revolvers were on frames originally intended for the .32 cartridge, they were referred to as the .38/.32 Terrier. The bottom revolver in the photo below is a very early postwar Terrier.
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| From top to bottom: J Magnum frame, J-frame, I-frame |
When Smith & Wesson started making small-framed .38 Special revolvers in the early Fifties, the cylinder window of the then-current Improved I-frame* was too small. To fix this, a new frame size was introduced: The J-frame. Essentially, the J was an Improved I-frame with a lengthened frame window to allow a longer cylinder to be fitted. They made J-frames and Improved I-frames side by side until the early Seventies when the Improved I was discontinued and all small-frame Smiths, regardless of the chambering, were made on J-frames. The middle revolver above is a Model 37 Chiefs Special Airweight from the mid-1970s.
Starting in 1996, Smith introduced yet another iteration of its small frame. Taurus had released its 5-shot small framed Model 605 in .357 Magnum in 1995 and S&W returned fire by offering .357 Magnum versions of its small frame. The existing cylinder window was again too small, and so the regular J-frame was supplanted by the "J Magnum" frame. The top revolver is a Model 432PD in .32H&R Magnum from the early 2000s, showing the longer cylinder window of the J Magnum frame.
*The difference between the I-frame and the Improved I-frame is that the latter used a coil mainspring like the later J-frame, rather than a flat leaf mainspring. The easiest way to tell them apart at a glance is to check the frontstrap for the presence of a strain screw. The coil mainspring guns won't have one.
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