Air rifle expert
There is no easy check you can perform at home, unless you have a bit of kit called a chronograph.
The latest types are battery operated, and cost around £40.
To use them you fit them over the muzzle and fire a pellet, then the internal electronics do all the mathematics for you and give you a readout.
They are claimed to be accurate within one per cent.
If your chronograph only tells you pellet speed, then you will have to weigh a pellet in grains, and apply the following formula:
Where V = the velocity in feet per second and W = the projectile weight in grains.
Muzzle energy in ft/lb =
V2 x W
64 x 7000
This formula applies to any projectile, not just an air rifle pellet.
If you use your rifle for hunting, a chronograph check will let you know which is the optimum pellet for your particular rifle.
The check is also useful if you have done any work on your rifle, like fitting a new spring. Then you can ensure that you are still within the legal limit.