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直吹(direct impingement)导气系统，原理是这样的：气体直接吹在枪机座上，冲击枪机座向后飞去，并且把多余的气体都喷在机匣里。类似工作原理的枪，有：Swedish Ljungman Ag m/42，Egyptian Rasheed Carbine and Hakim Rifle，French MAS-49，等等.这里有详细的介绍：
https://en.wikipedia.org/wiki/Direct_impingement
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很多人以为AR的工作原理是“直吹”，这其实是很大的误解。wiki里解释的很清楚：
The AR action designed by Eugene Stoner is commonly called a direct impingement system, but it does not utilize a conventional direct impingement system. In U.S. Patent 2,951,424, Stoner states that the system is not a conventional impinging gas system: ″This invention is a true expanding gas system instead of the conventional impinging gas system.″[2] Gas is routed from a port in the barrel directly to a chamber formed in the bolt carrier. 翻译一下： 斯通纳设计的AR的枪机，经常被称作“直吹”系统，但是它并不是传统的直吹系统。在相关专利里，斯通纳说，该系统不是传统直吹系统：“该发明是真正的气体膨胀系统而不是传统的（直接）冲击系统。” 气体从枪管的导气孔，被导入枪机座(bolt carrier)内部的一个气室中。
也就是说，虽然从外面看，AR气体被导回了机匣，很像“直吹”，但是它的工作原理，并不是气体直接把枪机座(bolt carrier)吹走。实际上，气体被导入一个气缸活塞系统，并且在里面膨胀，推动气缸和活塞之间的相对运动。整个气缸和活塞系统，都是在枪管同轴线上运动。
上面这个图里就可以看出来，气体的膨胀过程：左面的枪机座(bolt carrier)，其实就是气缸，而右面的枪机(bolt)，其实就是活塞。相对的来看，气缸和活塞是在往相反方向运动。但气缸的惯性大，气体膨胀结束后，所有零件整体后退。
Armalite公司（AR叫做Armalite Rifle)的技术文档里也写到了类似的内容，里面指出，AR普遍被错误的叫做“直吹”系统，更正确的叫法是“内活塞”(internal piston)系统，而普通的系统，是“外活塞”(external piston)设计。“直吹”名称的普遍误用，导致了大部分人对AR基本原理的误解。
Technical Note 54, Direct Impingement versus Piston Drive
Purpose: To compare the merits of internal and external piston drive systems.
Facts: The AR-15/M16 and the AR-10 family of rifles employ a unique gas powered operating system patented by Eugene Stoner in the 1950s. This gas operating system works by passing high pressure propellant gasses tapped from the barrel down a tube and into the carrier group within the upper receiver, and is commonly but incorrectly referred to as a "direct impingement" system.
The gas expands within a donut shaped gas cylinder within the carrier. Because the bolt is prevented from moving forward by the barrel, the carrier is driven to the rear by the expanding gasses and thus converts the energy of the gas to movement of the rifle's parts. The bolt bears a piston head and the cavity in the bolt carrier is the piston sleeve. It is more correct to call it an "internal piston" system.
Most previous semiautomatic rifles use an "external piston" system operating in a gas cylinder mounted outside the receiver, but instead attached to the barrel. Propellant gasses expand within the cylinder and force the piston to the rear. The piston either contacts a rod that and drives a carrier to the rear (FAL), or are part of, connected to, or strike a rod segment that passed around the action to cam and move the bolt (M1, M14, AK- 47, SCAR). In some cases the piston is fixed and the movable cylinder drives the rod (AR-180).
Advantages and disadvantages.
The Stoner system provides a very symmetric design that allows straight line movement of the operating components. This allows recoil forces to drive straight to the rear. Instead of connecting or other mechanical parts driving the system, high pressure gas performs this function, reducing the weight of moving parts and the rifle as a whole.
In external piston systems, the path of the operating force is mechanically shifted around the action, resulting in a considerable mass of moving parts moving outside the centerline of the firearm and producing various torques within the system.
There is a common belief that the external piston operated systems are less accurate than the Stoner internal piston system because the operating parts start moving while the bullet is still in the bore. This is not true: Army Ordnance tests conducted in the 1960s revealed that the bullet is 25 feet out of the bore of the M1 and 15 feet out of the bore of the M14 before any operating part begins to move. It is more likely that the imbalances of the external piston, operating rod, cylinder, and other parts hanging on the barrel produce disruptive vibrations as the bullet exits the bore.
Although movement of the operating parts while the bullet is in the bore isn't apparently a culprit in reducing the accuracy of external piston systems, the inherent accuracy of the Stoner internal piston system has been consistently confirmed in competitive shooting. In all events that allow use of any mechanism the shooter wishes, the Stoner internal piston system is prevailing. Few competitive shooters use the Garand or Kalashnikov systems, and none observed now use the FAL system. In American Service Rifle and NRA competition, the external-piston operated rifles are considered a significant disadvantage.
There is a debate about which system remains cleanest. The internal piston system tends to leave propellant residue in the receivers, while the external piston systems keep the residue outside the action in the cylinder. External piston driven systems, however, tend to allow more external dirt into the action because of the openings required for various connecting members (operating rod, bolt lugs, etc). Comparison tests of the M16 and the M-14 before Desert Storm confirmed the superiority of the Stoner system in sand and dust tests, and recent testing has proven that proper cleaning of either system provides excellent reliability.
ArmaLite concludes that there is no technical advantage to an external piston system employing current ammunition. It will likely, however, provide external-piston systems to the market as customers demand.
As a last note, misuse of the term "direct impingement" to describe the Stoner system is so common that it has confused the issue. A direct impingement system like that of the AG-42 Ljungman or the French MAS-49 rifle taps gas at the barrel and passes it into the receiver in a way similar to the M16, (the source of the confusion) but deposits it into a small, shallow cup or pocket in the carrier. The gas expands there and drives the carrier to the rear with relatively little pneumatic advantage. The addition of the Stoner internal piston system provides significantly more pneumatic advantage to the rifle and little of the blast of escaping gas at the breech end of the gas tube of the earlier rifles.
MARK A. WESTROM
President
有人说，把AR的枪机(bolt)叫做活塞，你是不是在做梦？太有想象力了？那么，让我们最后来看一看真相，AR的枪机(bolt)和SCAR的活塞(piston)长的都是什么样子的。。。
这个是AR的枪机，左边的那个箭头指的地方，其实就是AR里面的“内活塞”，上面带有三个活塞闭气环：
这个是著名“高大上活塞枪”，SCAR的活塞，左边箭头指的地方，是SCAR上面的活塞环。（这个图里显示的是活塞环损坏的情况，半个活塞环脱落了下来）
正常的AR活塞，和SCAR活塞，都带有三个活塞闭气环，维护方法是一样的：装回去之前，要把三个缺口转到错开的位置。
从这些图里就看到了。。。AR是一点不打折的活塞枪，活塞部分的设计，和SCAR是很像的，都带有三个活塞闭气环。AR活塞其实就长在枪机后面，每打一枪，不但所有零件在枪管轴线上运作，而且枪机在旋转开锁的过程中，受到一个向前推的力，这是内活塞AR设计最为独特的一个地方：这个前推力，一定程度抵消了枪膛里的压力，是巧合天工的设计，让旋转开锁变得容易。普通的外活塞设计，旋转开锁是粗暴向后拉扯，开锁要更费劲，磨损要更严重。
也有人说了，我的新AR，BCG很紧很涩啊，是不是次品啊。。。come on，这说明你的活塞环够紧，闭气效果肯定好，这和汽车发动机一样，都是要磨合的，汽车发动机里气缸活塞的磨合，和AR的磨合一样，都是在磨活塞环。。。多上点机油，使劲拉拉转速，跑一跑，就运作顺畅了
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发表于 2016-3-17 21:59
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