page_title: Blowback (firearms)
section_title: Roller-delayed
hierarchical_section_title: Blowback (firearms) / Delayed blowback / Roller-delayed
caption_attribution_description: Deutsch: Aufgeschnittenes Patronenlager mit Rollenverschluss des G3 Gewehrs English: Cutaway model of the chamber with gas relief flutes (left) and roller-delayed action of the G3 assault rifle n
context_page_description: Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gas created by the ignition of the propellant charge.
  Several blowback systems exist within this broad principle of operation, each distinguished by the methods used to control bolt movement. In most actions that use blowback operation, the breech is not locked mechanically at the time of firing: the inertia of the bolt and recoil spring, relative to the weight of the bullet, delay opening of the breech until the bullet has left the barrel. A few locked breech designs use a form of blowback to perform the unlocking function.
  The blowback principle may be considered a simplified form of gas operation, since the cartridge case behaves like a piston driven by the powder gases. Other operating principles for self-loading firearms include blow forward, gas operation, and recoil operation.
context_section_description: Roller-delayed blowback was first used in Mauser's Gerät 06H prototype. Roller-delayed blowback operation differs from roller-locked recoil operation as seen in the MG 42 and gas operated roller locked, as seen in the Gerät 03 and Gerät 06. Unlike the MG 42, in roller-delayed blowback the barrel is fixed and does not recoil, and unlike the Gerät 03 and Gerät 06 and StG 44, roller-delayed blowback systems lack a gas piston. These omissions are conducive to relatively light construction by significantly reducing the number of parts required and the amount of machining required to produce a rifle. As the bolt head is driven rearward, rollers on the sides of the bolt are driven inward against a tapered bolt carrier extension. This forces the bolt carrier rearward at a much greater velocity and delays movement of the bolt head. The primary advantage of roller-delayed blowback is the simplicity of the design compared to gas or recoil operation.
  The roller-delayed blowback firearm action was patented by Mausers Wilhelm Stähle and Ludwig Vorgrimler. Though appearing simple its development during World War II was a hard technical and personal effort, as German engineering, mathematical and other scientists had to work together on a like-it-or-not basis led by Ott-Helmuth von Lossnitzer, the director of Mauser Werke's Weapons Research Institute and Weapons Development Group. Experiments showed roller-delayed blowback firearms exhibited bolt-bounce as the bolt opened at an extreme velocity of approximately 20 m/s (66 ft/s) during automatic fire. To counter bolt-bounce the perfect angle choice on the nose of the bolt head had to be found to significantly reduce the opening velocity of the bolt. The extremely high bolt carrier velocities problem was not solved by trial and error. Mathematician Dr. Karl Maier provided analysis of the components and assemblies in the development project. In December 1943 Maier came up with an equation that engineers used to change the angles in the receiver to 45° and 27° on the locking piece relative to the longitudinal axis reducing the bolt-bounce problem. With these angles the geometrical transmission ratio of the bolt carrier to the bolthead became 3:1, so the rear bolt carrier was forced to move 3 times faster than the bolthead. The rearward forces on the bolt carrier and receiver were 2:1. The force and impulse transmitted to the receiver increases with the force and impulse transmitted to the bolt carrier. Making the bolt carrier heavier lessens the recoil velocity. For Mausers StG 45(M) project Maier assumed a 120 g (4.2 oz) bolt head and 360 g (12.7 oz) bolt carrier (1 to 3 ratio). The prototype StG 45 (M) assault rifle had 18 longitudinal gas relief flutes cut in the chamber wall to assist the bloated cartridge casing from the chamber walls during extraction. Fluting the end of the chamber provides pressure equalization between the front outer surface of the cartridge case and its interior and thus ensures extraction without tearing the case making extraction easier and more reliable. In 1944 other German companies like Großfuß, Rheinmetall and Haenel showed interest in developing roller-delayed blowback small arms. Großfuß worked on a roller-delayed blowback MG 45 general-purpose machine gun that, like the StG 45 (M), had not progressed beyond the prototype stage by the end of World War II.
  After World War II, former Mauser technicians Ludwig Vorgrimler and Theodor Löffler perfected the mechanism between 1946 and 1950 while working for the French small arms manufacturer Centre d'Etudes et d'Armament de Mulhouse (CEAM). In 1950 Ludwig Vorgrimler was recruited to work for CETME in Spain. The first full-scale production rifle to utilize roller-delay was the Spanish CETME battle rifle, which was closely followed by the Swiss SIG SG 510 and the CETME Model B-based Heckler & Koch G3. The G3 bolt features an anti-bounce mechanism that prevents the bolt from bouncing off the barrel's breech surface. The G3's "bolt head locking lever" is a spring-loaded claw mounted on the bolt carrier that grabs th
caption: Cutaway model of the chamber with gas relief flutes (left) and roller-delayed action of the G3 assault rifle
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