Recoil
Recoil (often called knockback, kickback or simply kick) is the
backward movement of a gun when it is discharged. In technical terms,
the recoil momentum acquired by the gun exactly balances the forward
momentum of the projectile and exhaust gases (ejecta), according to
Newton's third law, known as conservation of momentum. In hand-held
small arms, the recoil momentum is transferred to the ground through
the body of the shooter; while in heavier guns such as mounted machine
guns or cannons, recoil momentum is transferred to the ground through
the mount.
In order to bring the rearward moving gun to a halt, the momentum
acquired by the gun is dissipated by a forward acting counter-recoil
force applied to the gun over a period of time after the projectile
exits the muzzle. To apply this counter-recoiling force, modern
mounted guns may employ recoil buffering comprising springs and
hydraulic recoil mechanisms, similar to shock absorbing suspension on
automobiles. Early cannons used systems of ropes along with rolling or
sliding friction to provide forces to slow the recoiling cannon to a
stop.
Recoil
Recoil buffering allows the maximum counter-recoil force to be
lowered so that strength limitations of the gun mount are not
exceeded.
Gun
Gun chamber pressures and projectile acceleration forces are
tremendous, on the order of tens of thousands of pounds per square
inch and tens of thousands of times the acceleration of gravity (g's),
both necessary to launch the projectile at useful velocity during the
very short travel distance of the barrel. However, the same pressures
acting on the base of the projectile are acting on the rear face of
the gun chamber, accelerating the gun rearward during firing.
Practical weight gun mounts are typically not strong enough to
withstand the maximum forces accelerating the projectile during the
short time the projectile is in the barrel, typically only a few
milliseconds. To mitigate these large recoil forces, recoil buffering
mechanisms spread out the counter-recoiling force over a longer time,
typically ten to a hundred times longer than the duration of the
forces accelerating the projectile. This results in the required
counter-recoiling force being proportionally lower, and easily
absorbed by the gun mount. Modern cannons also employ muzzle brakes
very effectively to redirect some of the propellant gasses rearward
after projectile exit. This provides a counter-recoiling force to the
barrel, allowing the buffering system and gun mount to be more
efficiently designed at even lower weight. "Recoilless" guns,
(recoilless rifle), also exist where much of the high pressure gas
remaining in the barrel after projectile exit is vented rearward
though a nozzle at the back of the chamber, creating a large
counter-recoiling force sufficient to eliminate the need for heavy
recoil mitigating buffers on the mount.
The same physics affecting recoil in mounted guns and cannons applies
to hand-held guns. However, the shooter's body assumes the role of gun
mount, and must similarly dissipate the gun's recoiling momentum over
a longer period of time than the bullet travel-time in the barrel, in
order not to injure the shooter. Hands, arms and shoulders have
considerable strength and elasticity for this purpose, up to certain
practical limits. Nevertheless, "perceived" recoil limits vary from
shooter to shooter, depending on body size, the use of recoil padding,
individual pain tolerance, the weight of the firearm, and whether
recoil buffering systems and muzzle brakes are employed. For this
reason, establishing recoil safety standards for small arms remains
challenging, in spite of the straight-forward physics involved.[1]
Contents
1 Recoil: momentum, energy and impulse
1.1 Momentum
1.2 Angular momentum
1.3 Energy
1.4 Including the ejected gas
2 Perception of recoil
3 Mounted guns
4 Misconceptions about recoil
5 See also
6 References
7 External links
Recoil: momentum, energy and impulse[edit]
Momentum[edit]
A change in momentum of a mass requires a force; according to Newton's
first law, known as the law of inertia, inertia simply being another
term for mass. That force, applied to a mass, creates an acceleration,
which when applied over time, changes the velocity of a mass.
According to Newton's second law, the law of momentum -- changing the
velocity of the mass changes its momentum, (mass multiplied by
velocity). It is important to understand at this point that velocity
is not simply speed. Velocity is the speed of a mass in a particular
direction. In a very technical sense, speed is a scalar (mathematics),
a magnitude, and velocity is a vector (physics), magnitude and
direction. Newton's third law, known as conservation of momentum,
recognizes that changes in the motion of a mass, brought about by the
application of forces and accelerations, does not occur in isolation;
that is, other bodies of mass are found to be involved in directing
those forces and accelerations. Furthermore, if all the masses and
velocities involved are accounted for, the vector sum, magnitude and
direction, of the momentum of all the bodies involved does not change;
hence, momentum of the system is conserved. This conservation of
momentum is why gun recoil occurs in the opposite direction of bullet
projection -- the mass times velocity of the projectile in the
positive direction equals the mass times velocity of the gun in the
negative direction. In summation, the total momentum of the system
equals zero, surprisingly just as it did before the trigger was
pulled. From a practical engineering perspective, therefore, through
the mathematical application of conservation of momentum, it is
possible to calculate a first approximation of a gun’s recoil
momentum and kinetic energy, and properly design recoil buffering
systems to safely dissipate that momentum and energy, simply based on
estimates of the projectile speed (and mass) coming out the barrel. To
confirm analytical calculations and estimates, once a prototype gun is
manufactured, the projectile and gun recoil energy and momentum can be
directly measured using a ballistic pendulum and ballistic
chronograph.
There are two conservation laws at work when a gun is fired:
conservation of momentum and conservation of energy.
Recoil
Recoil is
explained by the law of conservation of momentum, and so it is easier
to discuss it separately from energy.
The nature of the recoil process is determined by the force of the
expanding gases in the barrel upon the gun (recoil force), which is
equal and opposite to the force upon the ejecta. It is also determined
by the counter-recoil force applied to the gun (e.g. an operator's
hand or shoulder, or a mount). The recoil force only acts during the
time that the ejecta are still in the barrel of the gun. The
counter-recoil force is generally applied over a longer time period
and adds forward momentum to the gun equal to the backward momentum
supplied by the recoil force, in order to bring the gun to a halt.
There are two special cases of counter recoil force: Free-recoil, in
which the time duration of the counter-recoil force is very much
larger than the duration of the recoil force, and zero-recoil, in
which the counter-recoil force matches the recoil force in magnitude
and duration. Except for the case of zero-recoil, the counter-recoil
force is smaller than the recoil force but lasts for a longer time.
Since the recoil force and the counter-recoil force are not matched,
the gun will move rearward, slowing down until it comes to rest. In
the zero-recoil case, the two forces are matched and the gun will not
move when fired. In most cases, a gun is very close to a free-recoil
condition, since the recoil process generally lasts much longer than
the time needed to move the ejecta down the barrel. An example of near
zero-recoil would be a gun securely clamped to a massive or
well-anchored table, or supported from behind by a massive wall.
However, employing zero-recoil systems is often neither practical nor
safe for the structure of the gun, as the recoil momentum must be
absorbed directly through the very small distance of elastic
deformation of the materials the gun and mount are made from, perhaps
exceeding their strength limits. For example, placing the butt of a
large caliber gun directly against a wall and pulling the trigger
risks cracking both the gun stock and the surface of the wall.
The recoil of a firearm, whether large or small, is a result of the
law of conservation of momentum. Assuming that the firearm and
projectile are both at rest before firing, then their total momentum
is zero. Assuming a near free-recoil condition, and neglecting the
gases ejected from the barrel, (an acceptable first estimate), then
immediately after firing, conservation of momentum requires that the
total momentum of the firearm and projectile is the same as before,
namely zero. Stating this mathematically:
p
f
+
p
p
=
0
displaystyle p_ f +p_ p =0,
where
p
f
displaystyle p_ f ,
is the momentum of the firearm and
p
p
displaystyle p_ p ,
is the momentum of the projectile. In other words, immediately after
firing, the momentum of the firearm is equal and opposite to the
momentum of the projectile.
Since momentum of a body is defined as its mass multiplied by its
velocity, we can rewrite the above equation as:
m
f
v
f
+
m
p
v
p
=
0
displaystyle m_ f v_ f +m_ p v_ p =0,
where:
m
f
displaystyle m_ f ,
is the mass of the firearm
v
f
displaystyle v_ f ,
is the velocity of the firearm immediately after firing
m
p
displaystyle m_ p ,
is the mass of the projectile
v
p
displaystyle v_ p ,
is the velocity of the projectile immediately after firing
A force integrated over the time period during which it acts will
yield the momentum supplied by that force. The counter-recoil force
must supply enough momentum to the firearm to bring it to a halt. This
means that:
∫
0
t
c
r
F
c
r
(
t
)
d
t
=
−
m
f
v
f
=
m
p
v
p
displaystyle int _ 0 ^ t_ cr F_ cr (t),dt=-m_ f v_ f =m_ p v_ p
where:
F
c
r
(
t
)
displaystyle F_ cr (t),
is the counter-recoil force as a function of time (t)
t
c
r
displaystyle t_ cr ,
is duration of the counter-recoil force
A similar equation can be written for the recoil force on the firearm:
∫
0
t
r
F
r
(
t
)
d
t
=
m
f
v
f
=
−
m
p
v
p
displaystyle int _ 0 ^ t_ r F_ r (t),dt=m_ f v_ f =-m_ p v_ p
where:
F
r
(
t
)
displaystyle F_ r (t),
is the recoil force as a function of time (t)
t
r
displaystyle t_ r ,
is duration of the recoil force
Assuming the forces are somewhat evenly spread out over their
respective durations, the condition for free-recoil is
t
r
≪
t
c
r
displaystyle t_ r ll t_ cr
, while for zero-recoil,
F
r
(
t
)
+
F
c
r
(
t
)
=
0
displaystyle F_ r (t)+F_ cr (t)=0
.
Angular momentum[edit]
For a gun firing under free-recoil conditions, the force on the gun
may not only force the gun backwards, but may also cause it to rotate
about its center of mass or recoil mount. This is particularly true of
older firearms, such as the classic Kentucky rifle, where the butt
stock angles down significantly lower than the barrel, providing a
pivot point about which the muzzle may rise during recoil.[citation
needed] Modern firearms, such as the M16 rifle, employ stock designs
that are in direct line with the barrel, in order to minimize any
rotational effects. If there is an angle for the recoil parts to
rotate about, the torque (
τ
displaystyle tau
) on the gun is given by:
τ
=
I
d
2
θ
d
t
2
=
h
F
(
t
)
displaystyle tau =I frac d^ 2 theta dt^ 2 =hF(t)
where
h
textstyle h
is the perpendicular distance of the center of mass of the gun below
the barrel axis,
F
(
t
)
textstyle F(t)
is the force on the gun due to the expanding gases, equal and
opposite to the force on the bullet,
I
textstyle I
is the moment of inertia of the gun about its center of mass, or its
pivot point, and
θ
displaystyle theta
is the angle of rotation of the barrel axis "up" from its orientation
at ignition (aim angle). The angular momentum of the gun is found by
integrating this equation to obtain:
I
d
θ
d
t
=
h
∫
0
t
F
(
t
)
d
t
=
h
m
g
V
g
(
t
)
=
h
m
b
V
b
(
t
)
displaystyle I frac dtheta dt =hint _ 0 ^ t F(t),dt=hm_ g V_
g (t)=hm_ b V_ b (t)
where the equality of the momenta of the gun and bullet have been
used. The angular rotation of the gun as the bullet exits the barrel
is then found by integrating again:
I
θ
f
=
h
∫
0
t
f
m
b
V
b
d
t
=
h
m
b
L
displaystyle Itheta _ f =hint _ 0 ^ t_ f m_ b V_ b ,dt=hm_ b L
where
θ
f
displaystyle theta _ f
is the angle above the aim angle at which the bullet leaves the
barrel,
t
f
displaystyle t_ f
is the time of travel of the bullet in the barrel and L is the
distance the bullet travels from its rest position to the tip of the
barrel. The angle at which the bullet leaves the barrel above the aim
angle is then given by:
θ
f
=
h
m
b
L
I
displaystyle theta _ f = frac hm_ b L I
The momentum of the ejected gases will not contribute very much to
this result, since the ejected gases have relatively low mass compared
to the bullet, and only that portion of gas exiting closely behind the
bullet has significantly high velocity to contribute to recoil
momentum. However, one should understand that total recoil momentum is
slightly more than the simple product of the mass and velocity of the
exiting projectile, for this reason.
Energy[edit]
A consideration of the energy released during the firing of a gun
leads to an additional equation useful in recoil analysis. Using
Newton's second law, force equals mass times acceleration, the energy
within a moving body due to its velocity change caused by that
acceleration can be stated mathematically from the translational
kinetic energy as:
E
=
1
2
m
v
2
=
p
2
2
m
displaystyle E= frac 1 2 mv^ 2 = frac p^ 2 2m
where:
E
displaystyle E,
is the translational kinetic energy
m
displaystyle m,
is the mass of the body
v
displaystyle v,
is its velocity
p
displaystyle p,
is its momentum (mv)
This equation is known as the "classic statement" and yields a
measurement of energy in joules (or foot-pound force in non-SI units).
E
t
displaystyle E_ t ,
is the amount of work (physics), force acting through a distance,
that can be done by the recoiling firearm, firearm system, or
projectile because of its momentum, and is also called the
translational kinetic energy. In the firearms lexicon, the energy of a
recoiling firearm can be described as "felt recoil", (what the shooter
literally feels from the force applied to the shooter's hand, arms and
shoulder during the distance the gun recoils to a stop), free recoil,
and recoil energy. This same energy equation applies to the projectile
exiting the barrel and is called: muzzle energy, bullet energy,
remaining energy. Further along on the trajectory, the energy of the
projectile at the point of impact is known as the down range energy or
impact energy and generally will be slightly smaller than the muzzle
energy due to wind resistance slowing the projectile.
Again assuming free-recoil conditions and assuming all forward
momentum is due to the projectile, the energy of the projectile will
be
E
p
=
p
p
2
/
2
m
p
displaystyle E_ p =p_ p ^ 2 /2m_ p
and the energy of the firearm due to recoil will be
E
f
=
p
f
2
/
2
m
f
displaystyle E_ f =p_ f ^ 2 /2m_ f
. Since, by Newton's third law,
p
f
+
p
p
=
0
displaystyle p_ f +p_ p =0
, it follows that the ratios of the energies is given by:
E
p
E
f
=
m
f
m
p
displaystyle frac E_ p E_ f = frac m_ f m_ p
The mass of the firearm (
m
f
displaystyle m_ f
) is generally much greater than the projectile mass (
m
p
displaystyle m_ p
) which means that most of the kinetic energy produced by the firing
of the gun is given to the projectile. (This, of course, is the design
intent, to deliver a projectile a great distance forward, as opposed
to sending a launcher uselessly rearward). The source of the kinetic
energy is the heat energy rapidly released during propellant
combustion. Rapidly burning propellant in a sealed container generates
tremendous pressure. Pressure is a force applied over an area; in this
case the base area of the projectile, driving the projectile down the
barrel at high speed. However, whereas momentum is balanced between
the projectile and the recoiling firearm, energy is not.
Energy
Energy of the
system is certainly conserved, conservation of energy, but in only the
general sense that all the energy in the system, kinetic and potential
energy, before the event equals all the energy after the event. That
is, some of the potential energy stored in the propellant is released
to create kinetic energy in the subsequently moving parts. Some of the
propellant energy, by creating high pressure and recoiling forces,
briefly deforms the barrel, gun mount, and projectile materials, which
heats these materials internally in the process. Additional excess
heat energy from the propellant escapes through the muzzle blast as
the hot gases exit behind the projectile. All of this heat energy,
that does not directly become system kinetic energy, slowly dissipates
into the atmosphere as the gun cools. Therefore, whereas momentum
between the gun and projectile balances, through conservation of
momentum, kinetic energy does not balance between the two. For
example, with a rifle weighing 5 pounds firing a 150 grain bullet, at
2840 feet per second, the recoil energy will be only about 0.43
percent of the total kinetic energy developed. The bullet receives
about 2685 foot-pounds of energy, and the rifle only 11.5 ft-lbs of
energy, even though the rifle and the bullet both receive about 1.89
pound-sec momentum. Given the following calculations:
convert the bullet and rifle weights to slug (mass)
the bullet: 150 grains/7000 grains per pound/32.17 ft/sec^2(g) =
.000666 slugs
the rifle: 5 lbs/32.17 = .155 slugs
calculate the bullet momentum first, as its velocity is easiest to
estimate from interior ballistics or directly measure at a firing
range:
Momentum
Momentum (bullet) = mass x velocity = .000666 x 2840 ft/sec = 1.89
pound-second
(Admittedly, calculations can be confusing with units of grains,
slugs, feet per second, pound-second, foot-pounds, etc., but
calculations have to use consistent units, (dimensional analysis),
even if inconsistent units are customary in casual conversation; for
example, stating the rifle weight in pounds but the bullet weight in
grains.)
Working backwards to find the recoil velocity of the rifle:
Momentum
Momentum (rifle) = 1.89 = .155 x V(rifle); V(rifle) = 12.2 ft/sec
Calculate bullet and rifle kinetic energy: 1/2 M V^2; 2685 foot-pounds
and 11.5 ft-lbs, respectively. Of the total kinetic energy developed
(2685 + 11.5), the rifle receives only 0.43%.
Understanding where all the energy goes during the combustion process
is important to properly designing gun and recoil systems. Recoil
energy is initially absorbed by the springs and hydraulic cylinders of
the buffering system, or the body of the shooter, which produces the
counter-recoil force. The kinetic energy of recoil is then slowly
dissipated as heat energy. For a hand-held firearm, the energy is
absorbed by the shooter's body, creating a small amount of heat in
muscles and bones. For the naval cannon from the figure above, it will
roll backwards and the recoil energy will be mostly absorbed by the
friction forces in the wheel axles and between the wheel and the ship
deck and this energy is again converted to heat.
Including the ejected gas[edit]
The backward momentum applied to the firearm is actually equal and
opposite to the momentum of not only the projectile, but the ejected
gas created by the combustion of the charge as well. Likewise, the
recoil energy given to the firearm is affected by the ejected gas. By
conservation of mass, the mass of the ejected gas will be equal to the
original mass of the propellant. As a rough approximation, the ejected
gas can be considered to have an effective exit velocity of
α
V
0
displaystyle alpha V_ 0
where
V
0
displaystyle V_ 0
is the muzzle velocity of the projectile and
α
displaystyle alpha
is approximately constant. The total momentum
p
e
displaystyle p_ e
of the propellant and projectile will then be:
p
e
=
m
p
V
0
+
m
g
α
V
0
displaystyle p_ e =m_ p V_ 0 +m_ g alpha V_ 0 ,
where:
m
g
displaystyle m_ g ,
is the mass of the propellant charge, equal to the mass of the
ejected gas.
This expression should be substituted into the expression for
projectile momentum in order to obtain more a more accurate
description of the recoil process. The effective velocity may be used
in the energy equation as well, but since the value of α used is
generally specified for the momentum equation, the energy values
obtained may be less accurate. The value of the constant α is
generally taken to lie between 1.25 and 1.75. It is mostly dependent
upon the type of propellant used, but may depend slightly on other
things such as the ratio of the length of the barrel to its radius.
Perception of recoil[edit]
Recoil
Recoil while firing Smith & Wesson Model 500 revolver
For small arms, the way in which the shooter perceives the recoil, or
kick, can have a significant impact on the shooter's experience and
performance. For example, a gun that is said to "kick like a mule" is
going to be approached with trepidation, and the shooter may
anticipate the recoil and flinch in anticipation as the shot is
released. This leads to the shooter jerking the trigger, rather than
pulling it smoothly, and the jerking motion is almost certain to
disturb the alignment of the gun and may result in a miss. The shooter
may also be physically injured by firing a weapon generating recoil in
excess of what the body can safely absorb or restrain; perhaps getting
hit in the eye by the rifle scope, hit in the forehead by a handgun as
the elbow bends under the force, or soft tissue damage to the
shoulder, wrist and hand; and these results vary for individuals. In
addition, as pictured on the right, excessive recoil can create
serious range safety concerns, if the shooter cannot adequately
restrain the firearm in a down-range direction.
Perception of recoil is related to the deceleration the body provides
against a recoiling gun, deceleration being a force that slows the
velocity of the recoiling mass.
Force
Force applied over a distance is
energy. The force that the body feels, therefore, is dissipating the
kinetic energy of the recoiling gun mass. A heavier gun, that is a gun
with more mass, will manifest lower recoil kinetic energy, and,
generally, result in a lessened perception of recoil. Therefore,
although determining the recoiling energy that must be dissipated
through a counter-recoiling force is arrived at by conservation of
momentum, kinetic energy of recoil is what is actually being
restrained and dissipated. The ballistics analyst discovers this
recoil kinetic energy through analysis of projectile momentum.
One of the common ways of describing the felt recoil of a particular
gun-cartridge combination is as "soft" or "sharp" recoiling; soft
recoil is recoil spread over a longer period of time, that is at a
lower deceleration, and sharp recoil is spread over a shorter period
of time, that is with a higher deceleration. Like pushing softer or
harder on the brakes of a car, the driver feels less or more
deceleration force being applied, over a longer or shorter distance to
bring the car to a stop. However, for the human body to mechanically
adjust recoil time, and hence length, to lessen felt recoil force is
perhaps an impossible task. Other than employing less safe and less
accurate practices, such as shooting from the hip, shoulder padding is
a safe and effective mechanism that allows sharp recoiling to be
lengthened into soft recoiling, as lower decelerating force is
transmitted into the body over a slightly greater distance and time,
and spread out over a slightly larger surface.
Keeping the above in mind, you can generally base the relative recoil
of firearms by factoring in a small number of parameters: bullet
momentum (weight times velocity), (note that momentum and impulse are
interchangeable terms), and the weight of the firearm. Lowering
momentum, lowers recoil, all else being the same. Increasing the
firearm weight also lowers recoil, again all else being the same. The
following are base examples calculated through the Handloads.com free
online calculator, and bullet and firearm data from respective
reloading manuals (of medium/common loads) and manufacturer specs:
In a
Glock 22
Glock 22 frame, using the empty weight of 1.43 lb
(0.65 kg), the following was obtained:
9 mm Luger:
Recoil
Recoil impulse of 0.78 lbf·s (3.5 N·s); Recoil
velocity of 17.55 ft/s (5.3 m/s);
Recoil
Recoil energy of
6.84 ft⋅lbf (9.3 J)
.357 SIG:
Recoil
Recoil impulse of 1.06 lbf·s (4.7 N·s); Recoil
velocity of 23.78 ft/s (7.2 m/s);
Recoil
Recoil energy of
12.56 ft⋅lbf (17.0 J)
.40 S&W:
Recoil
Recoil impulse of 0.88 lbf·s (3.9 N·s); Recoil
velocity of 19.73 ft/s (6.0 m/s);
Recoil
Recoil energy of
8.64 ft⋅lbf (11.7 J)
In a Smith & Wesson .44 Magnum with 7.5-inch barrel, with an empty
weight of 3.125 lb (1.417 kg), the following was obtained:
.44 Remington Magnum:
Recoil
Recoil impulse of 1.91 lbf·s (8.5 N·s);
Recoil
Recoil velocity of 19.69 ft/s (6.0 m/s);
Recoil
Recoil energy of
18.81 ft⋅lbf (25.5 J)
In a Smith & Wesson 460 7.5-inch barrel, with an empty weight of
3.5 lb (1.6 kg), the following was obtained:
.460 S&W Magnum:
Recoil
Recoil impulse of 3.14 lbf·s (14.0 N·s);
Recoil
Recoil velocity of 28.91 ft/s (8.8 m/s);
Recoil
Recoil energy of
45.43 ft⋅lbf (61.6 J)
In a Smith & Wesson 500 4.5-inch barrel, with an empty weight of
3.5 lb (1.6 kg), the following was obtained:
.500 S&W Magnum:
Recoil
Recoil impulse of 3.76 lbf·s (16.7 N·s);
Recoil
Recoil velocity of 34.63 ft/s (10.6 m/s);
Recoil
Recoil energy of
65.17 ft⋅lbf (88.4 J)
In addition to the overall mass of the gun, reciprocating parts of the
gun will affect how the shooter perceives recoil. While these parts
are not part of the ejecta, and do not alter the overall momentum of
the system, they do involve moving masses during the operation of
firing. For example, gas-operated shotguns are widely held to have a
"softer" recoil than fixed breech or recoil-operated guns. (Although
many semi-automatic recoil and gas-operated guns incorporate recoil
buffer systems into the stock that effectively spreads out peak felt
recoil forces.) In a gas-operated gun, the bolt is accelerated
rearwards by propellant gases during firing, which results in a
forward force on the body of the gun. This is countered by a rearward
force as the bolt reaches the limit of travel and moves forwards,
resulting in a zero sum, but to the shooter, the recoil has been
spread out over a longer period of time, resulting in the "softer"
feel.[2]
Mounted guns[edit]
Real kickback of a canon (Exposed in the Morges Castle, Switzerland)
Recoilless designs allow larger and faster projectiles to be
shoulder-launched.
A recoil system absorbs recoil energy, reducing the peak force that is
conveyed to whatever the gun is mounted on. Old-fashioned cannons
without a recoil system roll several meters backwards when fired.
First was introduced in Russia as Baranovsky gun pl:Oporopowrotnik by
Wladimir Baranovsky ru:Барановский, Владимир
Степанович in 1872 (short recoil operation) and later in
France (based on Baranovsky construction) - 75mm field gun of 1897
(long recoil operation). The usual recoil system in modern
quick-firing guns is the hydro-pneumatic recoil system. In this
system, the barrel is mounted on rails on which it can recoil to the
rear, and the recoil is taken up by a cylinder which is similar in
operation to an automotive gas-charged shock absorber, and is commonly
visible as a cylinder mounted parallel to the barrel of the gun, but
shorter and smaller than it. The cylinder contains a charge of
compressed air, as well as hydraulic oil; in operation, the barrel's
energy is taken up in compressing the air as the barrel recoils
backward, then is dissipated via hydraulic damping as the barrel
returns forward to the firing position. The recoil impulse is thus
spread out over the time in which the barrel is compressing the air,
rather than over the much narrower interval of time when the
projectile is being fired. This greatly reduces the peak force
conveyed to the mount (or to the ground on which the gun has been
emplaced).
In a soft-recoil system, the spring (or air cylinder) that returns the
barrel to the forward position starts out in a nearly fully compressed
position, then the gun's barrel is released free to fly forward in the
moment before firing; the charge is then ignited just as the barrel
reaches the fully forward position. Since the barrel is still moving
forward when the charge is ignited, about half of the recoil impulse
is applied to stopping the forward motion of the barrel, while the
other half is, as in the usual system, taken up in recompressing the
spring. A latch then catches the barrel and holds it in the starting
position. This roughly halves the energy that the spring needs to
absorb, and also roughly halves the peak force conveyed to the mount,
as compared to the usual system. However, the need to reliably achieve
ignition at a single precise instant is a major practical difficulty
with this system;[3] and unlike the usual hydro-pneumatic system,
soft-recoil systems do not easily deal with hangfires or misfires. One
of the early guns to use this system was the French 65 mm mle.1906; it
was also used by the World War II British
PIAT
PIAT man-portable anti-tank
weapon.
Recoilless rifles and rocket launchers exhaust gas to the rear,
balancing the recoil. They are used often as light anti-tank weapons.
The Swedish-made Carl Gustav 84mm recoilless gun is such a weapon.
In machine guns following Hiram Maxim's design - e.g. the Vickers
machine gun - the recoil of the barrel is used to drive the feed
mechanism.
Misconceptions about recoil[edit]
Hollywood
Hollywood and video game depictions of firearm shooting victims being
thrown several feet backwards are inaccurate, although not for the
often-cited reason of conservation of energy, (which would also be in
error because conservation of momentum would apply). Although energy
(and momentum) must be conserved (in a closed system), this does not
mean that the kinetic energy or momentum of the bullet must be fully
deposited into the target in a manner that causes it to fly
dramatically away.
For example, a bullet fired from an
M16 rifle
M16 rifle has approximately 1763
Joules of kinetic energy as it leaves the muzzle, but the recoil
energy of the gun is less than 7 Joules. Despite this imbalance,
energy is still conserved because the total energy in the system
before firing (the chemical energy stored in the propellant) is equal
to the total energy after firing (the kinetic energy of the recoiling
firearm, plus the kinetic energy of the bullet and other ejecta, plus
the heat energy from the explosion). In order to work out the
distribution of kinetic energy between the firearm and the bullet, it
is necessary to use the law of conservation of momentum in combination
with the law of conservation of energy.
The same reasoning applies when the bullet strikes a target. The
bullet may have a kinetic energy in the hundreds or even thousands of
joules, which in theory is enough to lift a person well off the
ground. This energy, however, cannot be efficiently given to the
target, because total momentum must be conserved, too. Approximately,
the fraction of energy transferred to the target (energy transferred
to the target divided by the total kinetic energy of the bullet)
cannot be larger than the inverse of the ratio of the masses of the
target and the bullet itself.
The rest of the bullet's kinetic energy is spent in the deformation or
shattering of the bullet (depending on bullet construction), damage to
the target (depending on target construction), and heat dissipation.
In other words, because the bullet strike on the target is an
inelastic collision, only a minority of the bullet energy is used to
actually impart momentum to the target. This is why a ballistic
pendulum relies on conservation of bullet momentum and pendulum energy
rather than conservation of bullet energy to determine bullet
velocity; a bullet fired into a hanging block of wood or other
material will spend much of its kinetic energy to create a hole in the
wood and dissipate heat as friction as it slows to a stop.
Gunshot victims frequently (but not always) simply collapse when shot,
which is usually due to psychological expectation when hit, a direct
hit to the central nervous system, or rapid blood pressure drop
causing immediate unconsciousness (see stopping power), or the bullet
shatters a leg bone, and not the result of the momentum of the bullet
pushing them over.[4]
See also[edit]
Recoil
Recoil operation, the use of recoil force to cycle a weapon's action
Ricochet, a projectile that rebounds, bounces or skips off a surface,
potentially backwards toward the shooter
Recoil
Recoil buffer
Muzzle brake
Recoil
Recoil pad
References[edit]
^ A Limited Performance Tradeoff Analysis of a Novel Closed-Breech,
Shoulder-Fired Weapon System, 1992; Appendix:
Recoil
Recoil in Shoulder-Fired
Weapons: A Review of the Literature, Robert J. Spine, US Army Human
Engineering Laboratory, 1982
^ Randy Wakeman. "Controlling shotgun recoil". Chuck Hawks.
^ "Soft
Recoil
Recoil System" (PDF). Field Artillery Bulletin. April 1969.
pp. 43–48.
^ Anthony J. Pinizzotto, Ph.D., Harry A. Kern, M.Ed., and Edward F.
Davis, M.S. (October 2004). "One-Shot Drops Surviving the Myth". FBI
Law Enforcement Bulletin. Federal Bureau of Investigation. CS1
maint: Multiple names: authors list (link)
External links[edit]
Recoil
Recoil Tutorial
Recoil
Recoil Calculator and summary of