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Joules is an formula to find energy of a moving object. This formula must use the metric system. Below is the formula

Kinetic Energy = 1/2 X Mass X Speed^2

Joules = .5*(KG(Meters per second))^2

BB weights are based on recommendations from joules. The recommended BB weights for is as follows:

Snipers

~480 FPS (~2.2 joules).36g

480-500 FPS (2.2-2.4 joules).4g

500-540 FPS (2.4-2.8 joules).43g

540-580 FPS (2.8-3.2 joules.45g

580-630 FPS (3.2-3.7 joules).5g

Assault

~340 FPS (~1 joule).2g

340-400 FPS (1-1.5 joules).25g

400-450 FPS (1.5-1.8 joules).28g

450-500 FPS (1.8-2.4 joules).32g

###### Joules

###### Joule Creep

Joule creep is a phenomenon where a gun will fire a particular joule (lets say 2) then, when a different (typically heavier) BB weight is fired from the same gun, no modifications made, the joules will increase (lets say 2.5). Joule creep is mostly caused by cylinder to barrel ratio. If the ratio is optimized for .45 gram BBs, .2 gram BBs will fire a far lower joule rating than .45 gram BBs will. If someone puts in .69 gram BBs in to a the same gun with a ratio optimized for .45 grams, the .69 gram BBs will also give a lower joule rating. ***more info coming***

If you would like to go into greater detail to see the joules for the bb weights/fps and the joules formula in action, check out the excel doc below.