If you’ve ever shot a gun, then you will have quickly learned the first fundamental rule of shooting: recoil sucks. Depending on the calibre, weight of the firearm, and your technique, just a few minutes of shooting something like a hunting rifle can quickly leave your shoulder bruised and sore. And the bigger the firearm, the worse the problem becomes, with large-calibre military artillery pieces requiring elaborate systems of hydraulic cylinders to absorb their prodigious recoil. This, in turn, makes these weapons extremely heavy and difficult to move around the battlefield. There are two basic solutions to this problem: mount the artillery on heavy armoured vehicles… or somehow eliminate the recoil itself. Over the last century, engineers around the world have devised dozens of ingenious methods to achieve just that, creating weapons that are simultaneously powerful and long-ranged while being light and compact enough to be moved around the battlefield by regular troops or light vehicles. This is the fascinating technology behind recoilless weapons. To begin with, let’s first examine the physics behind recoil. One way to understand this phenomenon is via Newton’s Third Law - that is, “For every action, there is an equal and opposite reaction.” A more useful principle, however, is conservation of momentum. Momentum, defined as an object’s ability to resist changes in motion, is given by the simple formula mass times velocity. When an object is split into pieces and those pieces propelled in different directions - such as in the case of a bomb exploding or, more relevant to our discussion, a firearm shooting a projectile - the momentum of the overall system is conserved. In other words, if you add up the momentum - mass times velocity - of every individual piece, they will sum up to the original momentum - in the case of a stationary object, zero. Most firearms shoot a projectile significantly lighter than themselves; however, as this projectile is travelling at a very high velocity, its momentum equals that of the firearm, which, being much heavier, will recoil at a significantly lower velocity. The heavier the firearm, the slower it recoils and vice-versa. This, along with surface area in contact with your shoulder, is why, despite sometimes being quite painful, the recoil of most firearms is nowhere near strong enough to actually rip your shoulder off - unlike the projectile being fired downrange. Based on this physical analysis, it stands to reason that if you placed two identical firearms back-to-back and fired them in opposite directions, their recoil would cancel out and the whole assembly would remain stationary. This is known as the counter-shot or counter-weight principle, and was the operating principle of the first recoilless firearm to see combat: the Davis Gun. Patented by U.S. Navy Commander Cleland Davis in 1914, the Davis gun was specifically intended for use aboard aircraft. During the First World War more conventional small-calibre cannons were experimentally fitted to various aircraft for use against balloons, zeppelins, ships, submarines, ammunition dumps, and other specialized targets; however, aircraft of the period were rather flimsy constructions of wood, wire, and canvas, and were easily damaged by the recoil of such weapons. Thus, by the end of the war both the American and British navies and flying services showed great interest in Davis’s design. The Davis Gun effectively comprised two gun barrels mounted back-to-back and fired a special double-ended cartridge. On firing, a conventional shell was propelled out the forward barrel towards the target, while an equivalent mass of lead shot and grease was expelled out the rear, the recoil of the two barrels cancelling each other out. Of course, standing directly behind what is effectively a gigantic shotgun is a good way to have a very bad day, meaning the Davis gun had to be rather awkwardly mounted at the very front of the aircraft with its barrel pointing downward at a steep angle so that the counter-shot was propelled safely up and over the top wing. There were other problems as well. Since the gun had to propel two projectiles at equal velocity, the propellant charge - and thus the cartridge - was much larger than usual, making it awkward to handle. Author: Gilles Messier Host/Editor: Daven Hiskey Producer: Samuel Avila Learn more about your ad choices. Visit megaphone.fm/adchoices