In experienced hands, the M-16 will never plunge into the mud, even if the shooter finds himself in it at the very top, never sips water and will always be cleaned and oiled.
Peter J. Cocalis.
As you know, all NATO fighters have experienced hands, high culture and at least one higher technical education. Therefore, the appearance of water in the receiver of their machines is excluded. Nevertheless, out of harm's way, European designers have begun converting the Stoner gas pipeline system to a piston one. The water hammer, disabling the weapon, and along the way the fighter, was ruled out by this decision, but life once again proved that if the wrong scheme was chosen at the very beginning, then no poultices could cure it.
The US Marine Corps stubbornly refuses to replace the good old pipelines with pistons. As it became known from a source, which I have no reason not to trust, the version of the piston model under the HK416 brand stubbornly does not want to work after being locked in water, and, you must agree, this is a significant factor for the Marine Corps.
Let's try to figure it out. In the video that we watched in the previous part, it is perfectly visible how the soaked arch after a few shots starts working normally. What happened? Hot gases trapped in the receiver and the cavity of the bolt carrier dried the water and thereby removed the obstacle to the normal operation of the weapon.
Let's take a look at the HK416 and AR-15 bolts and compare their contact areas with the bolt carrier:
The contact area in the German machine gun is several times larger than in the American one. When the lubricant burns out or is triggered in this place and water, carbon deposits or dust gets in instead of it, an abrupt change in the friction coefficient will occur, and hence the appearance of all kinds of failures during operation, both in the roll-forward and rollback mode of the bolt carrier. The most amazing thing is how the Germans made such a blatant miscalculation at all. Those interested can independently search for an image of the MP-18 shutter for comparison. That is, even at the dawn of weapon automation, German designers and Hugo Schmeisser, in particular, understood that the cylindrical shutter in the tubular casing would be overwritten and therefore the contact area with it was limited by narrow beads.
Perhaps we'll finish with wet cases. Let's move on to the dusty ones.
Dust resistance
Here is an interesting presentation on the results of dust tests carried out in 2007 by the Army Test and Evaluation Center (ATEC) of four models of automatic machines built according to the Stoner scheme: M4, XM8, MK16 SCAR and HK416. You can read about these tests in Russian here. Three models XM8, MK16 SCAR and HK416 have a piston arrangement. Let's see the resulting table right away:
FXT is a problem when extracting a cartridge case from a chamber. As you can see, the champion of such delays is the M4 gas pipeline system with a score of 271. Wait gloat that for the XM8, HK416 and MK16 this number is 9, 3 and 1, respectively. Such an excellent indicator is explained only by the fact that the unlocking impulse is transmitted to the bolt carrier faster and, possibly, even more powerful due to the rigid piston kinematics instead of the soft gas one. But then the shutter must experience greater pressure on its stops and a tendency to increase the mirror gap, respectively. Dust trapped in the barrel and braking the bullet already increases the pressure above normal. As a result, liner breaks for M4, XM8, HK416 and MK16 - 1, 10, 3, 7, respectively.
In my opinion, it is better to have twenty delays in the M16 than one case break in the MK16 SCAR and be unarmed. I will not deny myself the pleasure of emphasizing that the document says in black and white about a weapon resource of 6,000 rounds. The figure, by the way, is empirical, it was obtained during the Second World War. Most likely, it was limited mainly by the survivability of the barrel, although I would not say that about the stormgower. Nevertheless, the production of short-range cartridges for the Stg-44 was oriented precisely at the rate of 6,000 per assault rifle. Currently, the technology of manufacturing barrels has made great strides. In terms of survivability, they are one and a half to two times higher than the assigned resource of the weapon. So, for the AK-74, this figure is 18,000 with an assigned resource of 10,000. The 6,000 indicator is the natural limit for a given cartridge + weapon complex when operated under normal conditions with normal care, cleaning and lubrication. I repeat, the figure is empirical, if desired, it can be slightly improved due to technology, materials, but for a jump-like transition, you need to change the design. Or a constructor.
Blinds
There is a very good trait in the Western mentality. They like to look for problems, formalize them in the form of succinct and savory slogans, then explain to themselves and others how to solve them and, most importantly, make money on it. At one time, such a slogan was a continuous reengineering of business processes. Those who are in the subject remembered and understood, and to the rest I can say nothing interesting, the problems of sexual minorities, for example, are about the same. They search for flaws in the Kalashnikov assault rifle in a similar way. For example, the gap that forms under the cover of the receiver after removing from the fuse is declared a "significant drawback", since stones, sand and other debris can get inside through it, which the "testers" will try hard to push inside the machine with a shovel and force to refuse him.
Of course, various panaceas are offered in this case. Here is one of them embodied in the machine called Galil ACE.
What can I say. Two parallel guide cutouts, perpendicular to the opening movement from the edge. The line of the location of the protrusions for the guide cutouts is below the line of application of the force of the opening flap - a skew is obtained. Pour sand between the flats of the shield and the body from the Negev desert for complete happiness. In short, the solution is not "ice". In this case, you need to make a rotating shutter. In fact, in designs according to the AK scheme, it is needed only for marketing.
In the history of the Kalashnikov assault rifle, the problem of dust protection was also solved with the help of a curtain. During the development and preparation for production of AKM, the problem of reliable operation of the machine with such a shutter was not solved, therefore its implementation was postponed indefinitely. The decision came by itself. In the process of working out the overall reliability of the machine, it began to pass dust test with an open (!) translator flap without any problems and the need for such a shield has disappeared by itself. By itself, the design of the curtain is not so complicated if you make it like in a stormgower or an arch. That is, it opens automatically, but closes manually. But in technology, and even more so in weapons, there should be no functions, the performance of which is not directly related to the main functioning. This is an axiom. Sooner or later, the fighter will not close the curtain and it will not fulfill its purpose. So our engineers at IWA, who designed the Galil ACE, made it auto-close just right. What the Israeli engineers did not succeed in was succeeded by the Kalashnikov in his single machine gun.
The PC works with an open shutter, so a dust cover is a must. And it works as it should - automatically, only when the cartridge case is ejected, the rest of the time it remains closed and does not require additional manipulation after the firing is stopped. I remember that to ensure reliable extraction of the cartridge case through a curtained window, Kalashnikov used high-speed filming. It was in those years!
Stoner took the design from Schmeisser with little or no rework. But let's take a look at the curtain in the stormgower:
Behind it you can see the space between the bolt carrier and the bolt, which is most sensitive to dirt. Therefore, the curtain is justified here. But the curtain just opens automatically, you need to close it with your hand. Considering, again, the high culture and discipline of the German soldier, one can agree with this. Or maybe just admit that the automatic closing task was too tough for Schmassser or Stumpel? So did Stoner.
And why is this curtain in the "arch" at all?
The gap between the body and the bolt carrier is even smaller than in the AK. If desired, this gap can be further sealed with a fluoroplastic spacer and without friction loss. There are unfortunate holes left through which the gas is vented. This is not a problem, I see at least two solutions for how you can make isolation for them. For obvious reasons, I will not present them here. But then another question arises - why then this curtain on piston circuits such as HK-416? The answer is not at all where it is expected. It does not lie directly in the engineering field. Perhaps in H&K they conducted experiments with weapons without a curtain and received several delays longer, but it is not clear why. Just looking at the bolt of the HK-416, remembering the story of the G36, one cannot help thinking about the loss of gun-making professionalism by German engineers and sliding towards "trivial" mechanical engineering.
