Quote Originally Posted by lensman57 View Post
External powwer adjusters in themselves are not illegal so long as they alter the power within the legal limits set for the gun. Brocock and some others have some sort of gimmicky power adjusters to enable them to reduce the power for shooting vermin within confined spaces by restricting the airflow . The one on S400/500 series of guns can dramatically incerase or decrease the power therefore they are illegal if direct access is provided to alter the power on the go . If the security cap has been removed the adjuster must be recapped after the adjustment for the regulator has been made. Better be safe here as we are dealing with a ' firearm'.
This might help or not:

https://shooting-the-breeze.com/thre...djusters.5150/


A.G
That was 2010 and all opinions, and I'm not sure any subsequent statute or case law has made the position any clearer.
For my own peace of mind I have ordered from E8ay an M3 security torx button head screw and I'll leave the special torx bit at home. Readily available air arms break head plugs would be nice but they don't seem to have a part number.