Never noticed it before but the trigger group of the HK, M-14 operate in the same manner as that of the AK.
As the bolt travels rearward, it compresses the recoil spring while simultaneously forcing the hammer back. The bolt is then propelled forward by the recoil spring. As the bolt travels forward, the hammer's forward movement is arrested by the secondary sear which catches on the rear hook of the hammer. The bolt engages the base of the fresh cartridge which was pushed up by the follower. The cartridge is chambered while the bolt is rotated into the locked position. At about this time, the secondary sear is "tripped" by the bolt. This causes the hammer to be released which then strikes the firing pin. The process is repeated until the gun is either empty or the shooter removes the finger from the trigger.