If you have a Gamo CFR, CFX  or Accu .177/.22  it likely has damaged seals even if its new.  The factory does not bother to deburr the cocking slots and holes in the tube so when they shove in the rotary breech the seals are almost always cut & sheared off.  There is also an edge on the barrel breech so every time you rotate you could be damaging that seal needless to say this will greatly reduce power and accuracy.  Gamo does not sell parts to the public, this kit includes seals specifically sized for the rotary breech both .177/.22 and are not available at hardware stores.  Breech seal is a durable urethane, the outer cylinder depending on when your gun was produced may require a thicker seal, we take out the guesswork by supplying both.  I can't stress enough that before you install these you must file all edges on the inside of the tube and breech, clean and lube to allow safe passage.  These guns are not hard to work on and the gains of a proper reseal can be dramatic.  Kit will include all seals required for the rotary breech as well as removal tools and links to help you.  GOOD LUCK!