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Origins of the Blowback System: Its Trials and Triumph

By Louis A. Garavaglia

If any autoloading system has proven itself over the past 100 years, that system is the simple blowback. It has worked with pocket pistols taking cartridges as diminutive as the 2.7mm Kolibri, and (in the case of the Model 1910 Winchester) with rifles firing a 250-grain bullet at a velocity of more than 1,850 feet per second. With special modifications, it has worked with even heavier loads. The writer’s Astra M600 pistol, a simple blowback chambered for the 9mm Luger cartridge, has fired well over a thousand rounds without a hitch. And some of these loads, packed in 25-round cartons with faded labels printed in an undecipherable language, ejected the fired cases, shall we say, vigorously. Moreover, a friend’s Astra M400 (the 600’s slightly bigger brother) has gone through several thousand rounds of the powerful 9mm Bergmann-Bayard cartridge, also without malfunction. Both guns still work well and give every promise of continuing to do so.

As many readers know, in a true blowback action the slide or bolt remains closed during the moment of high pressure chiefly because of its mass and consequent inertia; there are no delaying or locking devices to hold it. Simply stated, the slide and bullet move away from each other upon discharge, but if the slide is, for example, 60 times as heavy as the bullet, then the slide’s rearward velocity is only about one-sixtieth of the bullet’s forward velocity, so the bullet has cleared the muzzle before the slide can open appreciably. (In the all-important initial stage of opening, incidentally, the recoil spring has little to do with this process.)

Again, few if any firearms designs have proven more successful than the blowback. As a Heckler & Koch brochure states the case: “Let us accept the fact that, when it comes to an automatic weapon bolt, a system consisting only of a mass and a spring cannot be surpassed for its simplicity and ruggedness.” But when the blowback system was first formally proposed, it met everything from strong skepticism to outright derision. Its designer, Capt....

This article first appeared in Small Arms Review V22N2 (February 2018)
and was posted online on December 22, 2017

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