The Quest for the Recoilless Gun
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
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