Foot Pounds of ENERGY (FPE)

This is also commonly referred to as 'muzzle energy' - 'stopping power' - or 'penetration power' in the powder burner world. But this is an 'aGun'(Airgun), so we will stick with FPE calculations. 

GrainsShot 1 @ 3,000 psi Max FPS (Feet Per Sec)Max FPE
(Foot Pounds of Energy)
~Shot 10 @/^ 2,000psiAvg. Minimum FPE
240g930 FPS461 fpe*~750 fps300 fpe
168g930 FPS322 fpe~750 fps210 fpe
120g930 FPS230 fpe~750 fps150 fpe
 82g930 FPS158 fpe~750 fps103 fpe

*I do not have a chronograph, and am relying on the reports of others for the FPS, and the 'calculator' for the fpe. Some have reported 930FPS max with the 82g pellet, whereas the same rifle - same fill - with the 145g Nosler supposedly clocked in at 800FPS, and a 212g single shot Air Venturi registered at 785 to 860FPS depending on the rifle, and how it is 'tuned.' Mine push out about 100psi per shot. 

All I know is the rifles I have HIT REAL HARD at 25 & 50 yards! 
Note: at distances up to 50 yards, it can still be an effective weapon down to about 650fps, which you should be able to get, even down to about 1,200psi.

To calculate the FPE, you'll need to know the speed of the projectile (fps), and weight of that projectile (grains), then you can determine muzzle velocity (FPE) from the kinematics equation, which is displayed as follows.

FPE = 1/2*m*v^2

Where FPE is foot pounds of energy (aka: kinetic energy)
m is mass (weight of projectile)
and v is velocity (speed of projectile)

Avg powder burning .357 shooting 158g bullet @1,235fps has 535fpe

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