Every time someone does a review of the Pedersen-designed Remington Model 51 and its "hesitation lock" design (which is not locked at all) they talk about how the separate breechblock allowed Remington to make the slide lighter and more compact or whatever.
I mean, I suppose that's a side-effect of the design, but it's certainly not the reason for it.
It's because when the Model 51 was introduced, Colt's Browning patent for a one-piece slide and breechblock that extended forward to enclose the barrel had yet to expire. That's the real reason why.
That's also the reason for the baroque method of attaching the 51's grip panels to the frame. That little pin at the heel of the grip gets pushed in to one side or the other and the grips are then slid down off the frame. Screws would have been much easier and cheaper, but the greatest firearms patent troll of the late 19th and early 20th Centuries had got there first.
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