In AK and M16, the same principle of operation of the automation is used - the removal of powder gases and the method of locking the shutter by turning it. This is where their similarity ends. First, let's take a look at the cartridges. Pay attention to the wider groove for the ejector hook and the shorter sleeve length of the domestic cartridge and the almost complete absence of the American taper (not to be confused with bottle-shaped). Consider the operation of the mechanisms in the rollback and rollback of the bolt carrier.
Rollback
Everyone knows the significant mass of the AK bolt carrier. It takes time and some free wheeling space to accelerate. In this acceleration, nothing prevents her, except for the return spring, unless the entire cavity of the receiver is clogged with dirt until it stops or you do not hold it by the cocking lever. But by the time the shutter is unlocked, it has already accumulated a certain amount of kinetic energy. Further, the very unlocking and straining of the liner takes place. I will describe the striking separately, since this process is not clearly described anywhere, neither in the NSD, nor on the forums of weapon hamsters. There will be food for the mind and trolling, so bear with it.
The residual pressure in the barrel by this time drops to an ugly low value. After breaking off the sleeve due to its taper, it no longer touches the chamber walls and does not rub against it at the time of extraction. Since nothing prevents the movement of the cartridge case from the chamber, the frame begins to spend its energy only on cocking the hammer, and then it still has enough strength to shake off the cartridges in the magazine with the shutter feeder and knock out the spent cartridge case. Thus, on one pulse received in the gas piston, the bolt carrier performs its functions in sequence.
The M16 automatics are much more complicated than in the AK. The gases discharged through the gas pipeline from the barrel into the cavity of the bolt carrier press against its rear wall and the end of the bolt, which at this time is under pressure in the opposite direction. The frame itself begins a horizontal displacement, and with a leading finger sliding one end in a figured cutout, turns the bolt, while cocking the hammer. Unlocking occurs very quickly due to the small angle of rotation of the bolt and the low inertia of the light frame, so at this moment there will be a residual pressure of several hundred atmospheres in the chamber.
The sleeve plays the role of a plunger displaced by the powder gases from the chamber. It presses on the bolt, giving it an additional impulse, and the ultra-small taper of its shape and the plasticity of the material provide reliable obturation. There is no straining here, and it is not needed. The sleeve rubs against the chamber walls all the way to the end of the exit. The scanty taper it still has is blown up by the residual pressure. The work of gases in the cavity of the bolt carrier stops immediately after the bolt is unlocked, and they are vented into the atmosphere through two side holes.
The undoubted advantage of this design is its compactness with a long sleeve (although the return spring had to be removed into the butt) and low weight. The process of operation of the M16 automatics is described in more detail in the Kalashnikov magazine N 8/2006 in an article by Ruslan Chumak, but not without inaccuracies.
But there is a place for entropy to roam. First, there are two sources of energy - gas impulses into the frame and into the sleeve blown out of the chamber. Secondly, several actions at the same time - unlocking the bolt, cocking the hammer, extracting the sleeve with overcoming its friction in the chamber. The programmers understood me immediately. Which program is easier to debug? The one in which the functions are executed sequentially, passing the result of their calculations, or the one in which several functions pass their values to several others, while working completely asynchronously. It is practically impossible to calculate possible failures in such a system. There are as many combinations of the state of the system depending on the pollution, weather conditions, the degree of stupidity of users, and the position of the weapon parts relative to each other, as well as types of malfunctions - from tight extraction of the cartridge case to its breakage; from skipping feed to jamming the cartridge; from the rupture of the receiver to the swelling of the barrel. There is simply not enough space to describe specific dependencies and consequences here.
Roll forward
Rolling the bolt carrier in the AK is easier to roll back. Only two consecutive operations - feeding the cartridge into the chamber from the magazine and turning the bolt. Please note that the frame accelerates well before starting its work, and its large mass by the end of the takeoff run, accumulates a good supply of kinetic energy, which practically all goes into closing the shutter. If it is not enough, hitting the cocking handle will solve all problems.
The M16 has a shorter bolt range and less mass and kinetic energy. And here is the frame at the end of its path, when the force of the return spring reaches a minimum value, and it itself has lost part of the reel energy to feed the cartridge, stumbles upon an unexpected obstacle - an ejector in the shutter.
This ejector has a very strong spring in order to send a spent cartridge case or an axial cartridge far away. But you need to squeeze it before turning the shutter. Frame energy or recoil spring force may not be sufficient if there is carbon or dirt. And now he is a universal shame - a jack-rammer. The trademark of the ar-shaped. A similar incident can be compared with the absence of an extractor in the first Bergman pistol. But Bergman is forgivable, he is a pioneer. And Stoner? Could, say, Stoner abandon the ejector and eject a liner like AK or Stg-44? Why didn't you? Complex issue. The answer, most likely, lies in that "irregularity" of which I spoke in the first part. It is practically impossible not only structurally, but also technologically to insert the reflector protrusion into the M16 shutter, as it is done in AK.
On a general philosophical topic, let's talk more, God bless someone, and as a bonus to what we have written, we will analyze one effect called "jamming".
Jamming
Take the AK bolt carrier, insert the bolt into it and bring it to the front position, as before installing it in the receiver. They occupy this position before the start of the roll-off. Press your finger into the shutter mirror, what happens? What should happen? Let's do the same with the M16. Oops. In and out, as Eeyore's donkey used to say.
On the roll, the AK bolt carrier pushes the bolt forward with a platform perpendicular to the movement. In the figure from the textbook, it is indicated under the letter "b" - a vertical platform. At the end of its movement, the left combat stop runs into the bevel inside the liner and turns the bolt, removing its leading protrusion (in the figure it is erroneously called "locking") from engagement with the "vertical" platform, and directs it to the bevel of the figured groove, which is actually begins to turn the shutter in a combat way.
The M16 has no vertical or perpendicular pads.
As conceived by the author, the frame pulls or pushes the bolt through the leading pin passing through the curved groove. What happens if the shutter starts to experience difficulty moving while rolling? The decelerating force will be transmitted through the pivot pin head to the receiver groove wall.
Here is a video that clarifies the experiment.
The bolt carrier and the bolt are clamped in the body in a counter movement, after which the weapon is placed on the end of the protruding frame. The experimenter, pressing the bolt with his finger, holds the machine in weight, due to the forces of friction between the cap of the leading finger and the groove for it. As soon as he removes the force on the bolt, the weapon falls under the influence of gravity. The beauty of such a constructive solution is that it is not limited to one defect. It can be triggered both in the run-up and rollback, and depending on pollution or energy loss at other nodes.
