With all the forces being
generated to propel the bullet out of the gun there
must be forces pushing in the opposite direction of
the bullet to satisfy Newton’s third Law of Motion,
“For every action there is an equal and opposite
reaction”. This is known as recoil.
Under the Law of Conservation of
Momentum, the total change in momentum must be zero.
For this to be true, there must be an equal amount
of momentum pushing back on your shoulder as is
pushing the bullet forward. The momentum on your
shoulder when a gun a gun kicks back is known as
recoil. To calculate the amount of recoil your
shoulder receives you can use the following equation
for calculating “felt” recoil.
According to the Sporting Arms
and Ammunition Manufactures Institute SAAMI
Calculating “felt” recoil is determined in the
following equation and example: * Note their
calculations were not done in SI units and this is a
direct quotation from their article so the below
calculations are given in standard no SI
measurements.
Example from SAAMI
SAAMI also does a great way
of relating how recoil is just kinetic energy so
that I can be calculated using 1/2 MV^2. This
example also shows why recoil is generated when a
firearm is discharged. As you can see the larger the
mass of the projectile the greater the felt recoil
because of momentum. Likewise, a lighter rifle will
increase the recoil because the weight of the
firearm is in the denominator so the larger of the
rifle the weight the smaller the felt recoil. I
include this example as it is a great illustration
of how recoil works. ALL Credit goes to SAAMI see
bibliography for article details.