I want to ensure that all of them are legal and do not exceed the legal limit.
Is there a standard pellet I should use for testing?
As the maximum energy law has been in force for around 50 years, there must surely be some standard tests and appropriate pellets.
Can you advise?
I wish I could give you an easy answer but, unfortunately, this is not a simple matter.
The current law states that if an air rifle is capable of producing a muzzle energy in excess of 12ft/lb, or 6ft/lb in the case of an air pistol, then it would be classified as a firearm and would be subject to a Firearms Certificate.
The Act does not specify how the energy test should be conducted, nor does it stipulate what type, size and weight of pellet or missile should be used in the test.
Furthermore, the material from which it should be produced, or any other specification of the equipment used in the test, is not specified either.
This is then further complicated by the fact that there are no established bore sizes for airgun barrels as there are for rifle and shotgun barrels.
My advice would be to use a waisted Diablo-shaped lead pellet of average weight, 7-gr to 8-gr for .177 or 4.5mm barrels, and a 14-gr to 15-gr pellet for .22 or 5.5mm barrels, with a 16-gr to 18-gr pellet for pre-1968 .22 with 5.6mm barrels.
These are the types of pellets which the rifles and pistols were intended to use when first produced.