[BlackDogAirsoft]

Nah man, a guy was dming me on Instagram about parts needed to build an 8j airsoft gun lol

I put an airsoft barrel on an airbow I made and got 39J.
That's above the speed of sound with a .48g BB.
Funnily enough, the BB reached a building 110m away barely faster than a 3J gun with the same ammo.

Quite literally this:

 

[BlackDogAirsoft]

It is a 33 grain projectile with 230 grains of powder. It travels at 5883 fps i.e. Mach 5.
In order to make the projectile not disintegrate special barrels have to be used: 3-groove, polygonal-rifling 1:20″-twist. The bullets are not jacketed but turned on a lathe.

As for the airsoft, 550 is the limit for the local fields.This was with .38g bbs, now I grabbed some .20, I will see what that is.

To be honest I would use the joules as a reference since you will presumably be shooting .38s anyway.