This kit contains most things needed to service BSA Mercury's spring guns.
The kit includes:
BSA Piston Oring Seal
BSA Piston Buffer Washer
BSA Breach Seal
Bisley Spring Grease
The kit can be used to service BSA Mercury's
Warning - replacing your air rifles mainspring may increase its power making it illegal. Redbeck Shooting Supplies would recommend that you seek manufacturers advice or a professional gunsmith before attempting to alter your rifle, and that you always check your rifles power using an accurate chronograph to ensure you stay within the law.