American Rifleman by Jeremiah Knupp 7/8/2023
John Browning’s tilting barrel design, which uses a link or cam surface to disengage the barrel’s locking surface from the slide, dominates the world of centerfire semi-automatic handguns. When announcing its new M&P 5.7 pistol earlier this year, Smith & Wesson touted the new handgun’s “Tempo Barrel System” that uses a gas-operated action that is locked with a rotating barrel. While Smith & Wesson’s design is innovative, the idea of using a rotating barrel in a semi-automatic pistol is not a new one and actually dates back to the birth of self-loading handguns in the 1890s. While always occupying a small niche of the handgun world, rotary-barrel pistols played an important role in firearms development and continue to offer innovative design features.
Rotating barrels are used for two purposes in semi-automatic pistols. The first is to delay a blowback-operated mechanism. Instead of just using the weight of the slide combined with a heavy spring to keep the breech closed until pressures have dropped to a safe level, a cam follower lug on the barrel works against a cam surface in a slide to slow the opening of the breech with the barrel’s rotation, allowing components, like the slide and mainspring, to be lighter. The second use of a rotating barrel is in a locked-breech mechanism. In this case, the barrel’s cam lug causes the barrel to rotate as it moves rearward, unlocking separate locking lugs (usually two, three or four) from a slide.
A rotary-barrel action in a semi-automatic handgun has several perceived benefits. The counter-rotational force of the bullet moving through the barrel’s rifling helps to keep the action closed. The rotating action of the barrel means that part of the force is being re-directed, rather than going straight back into the shooter’s hand. The linear movement of the barrel also minimizes muzzle rise. Accuracy is theoretically better, as the barrel stays on the same linear plane as slide-mounted sights. In a locked rotary-barrel design, symmetrical locking lugs around the circumference of the barrel make for a strong action that spreads out the locking forces in an equal pattern. It also allows for a pistol to have a lower bore axis, as the barrel doesn’t need room to drop as it tips to unlock, again contributing to recoil control.
The system also has its drawbacks. A slide tends to be wider to accommodate the locking lug arrangement in locked-breech pistols. Manufacturing a rotary-barrel pistol, especially in early designs, was more complex. And it is problematic to mount a screwed-on suppressor to the muzzle end of the barrel, as the barrel’s rotating action tends to loosen it.
Early semi-automatic handguns experimented with a variety of action types, from the toggle breech of the Luger to rifle-like sliding bolts on designs like the Mauser C96 “Broomhandle.” Austro-Hungarian engineer Karel Krnka was experimenting with long-recoil designs, in which a rotating bolt locked into a barrel and both recoiled together before unlocking. By the early 1900s, Krnka’s designs had evolved to use a rotating barrel that locked inside of a slide.
As Krnka continued to refine his design, he paired with Viennese industrialist Georg Roth. Roth was in the midst of trying to develop a semi-automatic handgun that would win adoption by the Austro-Hungarian empire. They would find success with the M1907 Roth-Steyr (Steyr being the manufacturer), which was adopted by the Austro-Hungarians for their cavalry and other select specialized units, marking the first major world power to adopt a semi-automatic handgun for its military land forces.
The Roth-Steyr was a magnificently machined pistol. The “slide” is formed by the breech bolt telescoping forward and forming a “sleeve” around the rotating barrel, the pair of which ride within the pistol’s frame. It is a short-recoil system in that the barrel and slide of the Roth-Steyr stay locked together at the moment of firing. As they move rearward together, helical grooves in the barrel bushing at the front of the frame act on two cam lugs near the barrel’s muzzle to cause the barrel to rotate and unlock two opposing lugs near the breech, so that the slide can unlock and continue rearward to cycle the action.
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Over a century after the first rotary pistols were being built in the Austro-Hungarian empire, the design’s history has come full-circle. Austrian company Glock, who used the half-cocked striker concept of the Roth-Steyr, has also adopted that design’s rotating barrel with the Glock 46. Nominally the size of the company’s Model 19, the Glock 46 was designed for a German police contract. Glock touts better accuracy and the lower bore axis of the rotary design and the pistol also has a unique striker mechanism that allows it to be disassembled without pulling the trigger. There are no plans to sell the pistol commercially.
While a design that will never dominate the semi-automatic handgun market, the rotary-barreled pistol labors on, and pistols like the S&W M&P5.7 show there is still room for innovation, with a twist.
More:
https://www.americanrifleman.org/content/rotary-barrel-pistols-a-design-that-has-come-full-circle/
