Muzzle velocity
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.
Muzzle energy
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.
It should be noted that in the case of saboted projectiles being simulated with the GGDT, the actual muzzle energy is equal to GGDT muzzle energy * projectile mass/projectile mass+sabot mass.
The following is a table of miscellaneous, rim, and centerfire ammunition muzzle energies, for comparison.
| Projectile | Energy, J |
| typical paintball | 17 |
| 0.22 rimfire | 180 |
| 2" Spud at 300FPS (moderate sized combustion spud gun) | ~400 |
| 0.45 colt | 675 |
| 410 slug | 1000 |
| 2" Spud at 490FPS (large sized combustion spud gun) | ~1100 |
| 2" Spud at 600FPS (moderate sized pneumatic spud gun) | ~1600 |
| 0.223 (M-16) | 1900 |
| 0.60 (M-14, M-60) | 3640 |
| 30-06 | 4500 |
