Muzzle velocity is the velocity of the projectile immediately after leaving the barrel, and other than a few hypothetical situations, is the fastest the projectile will ever go. Muzzle velocity is typically measured by a chronograph, a device that measures the time it takes the projectile to travel between 2 sensors, although less accurate results can be gathered from a ballistic pendulum or the quite inaccurate hang time test.
This is muzzle velocity's companion, and can be calculated as following: (1/2)(Mass)(Velocity2), where mass is in kilograms, velocity is in meters/sec, and output is in Joules. For instance, a 100g (0.1Kg) potato going 150 meters/sec (a large combustion spud gun is capable of this) would have a muzzle energy of: (1/2)*(0.1Kg)*(150m/s)2=1125 J.
1.5 joules is approximately 1 foot pounds, the traditional imperial (US) unit of energy for firearms.
The following is a table of miscellaneous, rim, and centerfire ammunition muzzle energies, for comparison.
|2" Spud at 300FPS|
(moderate sized combustion spud gun)
|2" Spud at 490FPS|
(large sized combustion spud gun)
|2" Spud at 600FPS|
(moderate sized pneumatic spud gun)
|0.60 (M-14, M-60)||3640|
|100g slug at 1300FPS|
(moderate sized 10x hybrid spud gun)