AN-94 "Abakan"
An interesting video about the Avtomat Nikonova 94, though it's in Russian...
The main reason I post this is because I remembered reading a description about the firing mechanism of the AN-94, and I just found the passage again in the book "The AK-47 and AK74 Kalashnikov Rifles and Their Variations" by Joe Poyer. On page 126:
"Almost as soon as the AK-74 was type-classified, GRAU began a study of small-arms technology to determine the range of operating systems to be tested to develop a new rifle that would meet accuracy, reliability, ease of manufacturing and other requirements. In the subsequen testing, the "blowback-shifted pulse (BBSP)" system ranked high.
In the BBSP system, the receiver/barrel assembly moves in opposition to the bolt/bolt carrier assembly. Gas from the burning propellant drives the bolt and its carrier independently of the receiver/barrel system during part of the firing cycle.The movement of both units is not to cancel the energy developed by either, but delay it so that the first two bullets have left the muzzle before the recoil impulse is felt.
The operating system of the AN-94 is placed within what the Russians refer to as the "carrier-stock." The receiver/barrel form one unit which moves back and forth on guide rails mounted in the stock. The bolt and its carrier function as a conventional unit and reciprocate within the receiver. To understand how the system operates, picture this:
1) When the trigger is pulled and the sear released, the firing pin strikes the cartridge, igniting the primer and powder.
2)The recoil from the cartridge starts the entire receiver/barrel assembly backward with the bolt and carrier locked into the breech.
3) As it moves, it compresses the buffer spring.
4) As the bullet passes the gas port in the barrel, expanding propellant gas bleeds out and back through a tube and strikes the face of the bolt carrier.
5) This accelerates the bolt/bolt carrier assembly backward than the receiver barrel assembly is traveling, and it turns the carrier in its cam rails to unlock the bolt from the breech, pull the expended cartridge out, and eject it.
6) The bolt/bolt carrier assembly then strikes a buffer and the recoil spring drives it forward.
7) The position of the receiver/barrel assembly and the bolt/bolt carrier assembly depresses the sear momentarily so that the bolt carrier passes over it and strips a new cartridge from the magazine.
8) The bolt carrier pushes the cartridge into the breech, which is still moving backward.
9) As the bolt locks closed in the receiver, the sear releases, the firing pin strikes the cartridge primer and the second round is fired.
10) The empty case is ejected and the bolt/bolt carrier assembly cycles again by the time the receiver/barrel assembly strikes against its buffer assembly and starts moving foward again.
11) The third round is fired when the receiver/barrel assembly moves forward because the disconnector moves with it and trips the sear to fire the third cartridge.
12) The barrel/receiver assembly now moves rearward once again - as with the first two shots - but the disconnector contacts a second shoulder on the trigger and holds there allowing the bolt/bolt carrier assembly to pass over and cam the bolt into battery.
13) The disconnector releases as the barrel/receiver assembly moves forward again and the fourth round is fired - unless the trigger has been released.
This design allows two bullets to leave the barrel while the receiver/barrel is still moving rearward. Since the heavier receiver/barrel has not yet stuck its buffer and the bolt/carrier is moving in opposition, the point of aim is not disturbed. The cyclic rate of this two-round burst has been measured at 1,800 rounds per minute. After the first two rounds are fired and if the trigger is not released, the rifle then continues to fire, but now at a slower 600 rpm. When the trigger is released, the cycle starts over again.
The "dwell" time between the second and third rounds is long enough that a trained shooter can easily fire two-round busts with great accuracy."
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