What is the difference between a hammer and a striker?
A hammer is a rotating body mounted on an axle that is usually (
but not always) separate from the firing pin. A striker is a linear-sliding body that usually (but not always) has the firing pin mounted directly to its front. Basically just a heavy firing pin that's driven by the mainspring directly.
(ETA: The mainspring being named so because, whether driving a striker or hammer, it's the spring that actually makes the gun fire.) Illustrated example. Many if not most recent semiauto pistols (including the Glock) and the overwhelming majority of bolt-action rifle designs all use strikers instead of hammers.
The thing on the upper-rear of those clandestine shotguns could be the top of a hammer, but it reminds me more of the striker cocking handles on the sides of various 37mm flare guns. It's also mounted kind of high to be a hammer, it would be at a mechanical disadvantage to driving the firing pin fast enough in that position.
It does seem odd though that the maker didn't include some kind of stud-and-cam type arrangement, having already done a substantial part of the work, but perhaps that required more sophisticated machining than he was equipped to do.
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I googled "cam stud operated revolver", and found this.
Yeah, English Webley-Fosbery, like GM said. That's exactly what I was talking about when I said...
. . .but there's no cam track on the outside of the cylinder. . .
Another and, in this case, even more relevant example is the Pancor Jackhammer, an aborted prototype
area denial weapon fully-automatic auto-revolver shotgun.
As for Ghost in the Shell, I've never read the manga, but in the first movie I don't remember it ever being stated definitively that Togusa's revolver was an
auto-revolver per se, and to me it looked more like a MATEBA 2006M - which was a conventional double-action, rather than an auto-revolver, with the 6 o'clock barrel. Sadly never made available in the states. I don't remember what his gun looked like in the series. Of course I don't think GitS did as good a job with guns in general as Cowboy Bebop (although fridge logic makes me wonder why the Bebop world has had almost no new gun designs in 70 years, I mean we've hit a technological plateau but not
that badly,) but then, I didn't watch it for the guns, I watched it for the writing.