In the gas-operated AR design, when does the bolt carrier begin to move backwards during the unlocking phase of the cycle of operations?
The correct answer and explanation is:
In the gas-operated AR design, the bolt carrier begins to move backwards during the unlocking phase of the cycle of operations immediately after the pressure from the expanding gas pushes the bolt carrier rearward. This happens when the gas enters the gas tube from the gas block, which is located just in front of the barrel.
As the projectile travels down the barrel, the gas pressure builds up and is diverted into the gas port. This gas travels through the gas tube to the gas key on the bolt carrier. The high-pressure gas pushes against the carrier, forcing it rearward. The backward movement of the bolt carrier unlocks the bolt from the chamber. The force generated by the expanding gas is enough to overcome the resistance of the locking lugs, which engage the barrel extension.
During this process, the bolt and carrier assembly travel rearward, ejecting the spent cartridge case in the process. As the carrier continues its movement, the recoil spring compresses, storing energy for the return stroke. This rearward movement helps to complete the cycle by extracting and ejecting the spent case and preparing the chamber for a new round.
This mechanism allows the AR to operate semi-automatically or fully automatically, depending on the configuration. In essence, the unlocking phase is part of the greater cycle, which includes gas operation, unlocking, extracting, ejecting, chambering a new round, and locking. The timing and synchronization of each phase are essential for the smooth operation of the rifle, ensuring reliable feeding, extraction, and ejection of rounds.