page_title: Heckler & Koch G3
section_title: Operating mechanism
hierarchical_section_title: Heckler & Koch G3 / Design details / Operating mechanism
caption_attribution_description: Cutaway view of the G3 style rifle's Roller delayed Blowback system.
context_page_description: The G3 is a 7.62×51mm NATO, select-fire battle rifle developed in the 1950s by the German armament manufacturer Heckler & Koch in collaboration with the Spanish state-owned design and development agency CETME.
context_section_description: The G3 is a selective-fire automatic weapon that employs a roller-delayed blowback operating system. The two-piece bolt assembly consists of a breech (bolt head) and bolt carrier. The bolt is held in battery by two sliding cylindrical rollers that engage locking recesses in the barrel extension. The breech is opened when both rollers are compressed inward against camming surfaces driven by the rearward pressure of the expanding gases upon the bolt head. As the rollers move inward, recoil energy is transferred to the locking piece and bolt carrier which begin to withdraw while the bolt head slowly moves rearward in relation to the bolt carrier. As the bolt carrier clears the rollers, pressure in the bore drops to a safe level, the bolt head is caught by the bolt carrier and moves to the rear as one unit, continuing the operating cycle.
  Based on the geometric relationship arising from the angles of the roller contact surfaces of the locking piece and the barrel extension recesses, the recoil of the bolt head is delayed by a ratio of 4:1 for the 7.62×51mm NATO chambering. Thus during the same period of time, the bolt head carrier moves 4 times faster than the bolt head. This ratio is continued until the locking rollers have been withdrawn from the barrel extension recesses.
  The bolt features an anti-bounce mechanism that prevents the bolt from bouncing off the barrel's breech surface. The "bolt head locking lever" is a spring-loaded claw mounted on the bolt carrier that grabs the bolt head as the bolt carrier group goes into battery. The lever essentially ratchets into place with friction, providing enough resistance to being re-opened that the bolt carrier does not rebound. The spring-powered claw extractor is also contained inside the bolt while the lever ejector is located inside the trigger housing (actuated by the recoiling bolt).
caption: A schematic of the G3 roller-delayed blowback mechanism
exif: {}