Blowback operation is usually found in pistols chambered for rounds smaller than 9mm Luger and in submachine guns such as the Swedish Carl Gustav, Sten, Uzi, and Gordon Ingram's MACs. While simple and reliable, in submachine gun applications blowback usually requires a strong recoil spring and relatively massive bolt. Combined with the usual open-bolt, fixed-striker firing mechanism this means the point of aim tends to shift when the bolt is released by the sear. (This is called firing from an open bolt since the entire bolt, rather than just a striker or hammer, is held back by the sear.)
Blowback submachine guns can require a lot of force to cock, given the usual short travel of the bolt. The stiff springs used also contribute to high cyclic rates which can mean rapid ammunition consumption and difficult control. Submachine guns are commonly used with shoulder stocks, straps, slings and/or forward grips to help ameliorate these tendencies.
In semi-automatic pistols of smaller calibers such as .22, .25 or .380 (9mm short), the operating forces are smaller, but smaller overall masses can diminish controllability. Inertia operated pistols are usually hammer or internal striker fired from a closed slide. This is a benefit in that there are no large masses moving around to upset aim when striker is released.
In the Uzi and other modern submachine guns the bolt wraps around the barrel, shortening overall length for a given bolt mass. In these guns the bolt moves inside a receiver. In most pistols, including the rare examples of machine pistols, a slide takes the place of the bolt, containing the striker, extractor, breech and bulk of the moving mass.
Some blowback machine guns fire from a closed bolt, improving first shot precision. Others have been made to leave the bolt open after the first round or string of automatic fire, improving cooling and reducing the possibility of cook-off. These features have operational advantages but also increase mechanical complexity. Added complexity is generally a liability in small arms design since it can reduce reliability. Simpler is usually better, so it's perhaps a tribute to persistence in development and use that more complex mechanisms have been made to perform effectively.
Next Section - Delayed Inertia
Back to Operating Systems Index
Back to Index