Remove the stock and front band. Then remove the existing barrel by undoing the barrel set screw (Part Number 2800) and pulling it straight out of the receiver. Insert the O rings in the guides dry, then apply a little moly over the rings and that part of the barrel which fits into the receiver before pushing them together. It may be necessary to de-burr and/or slightly chamfer the front of the receiver in order to accept the replacement barrel without tearing the O rings as this WILL cause a loss of muzzle velocity. You should use new O rings every time you re-install a barrel in the receiver. Don't forget to use the high-quality replacement set screw! The original set screw is removed using the metric Allen wrench supplied with the gun, the replacement set screw is tightened with a 3/32-inch wrench. Do not order unless you understand what you are getting in to! Specially packaged by Archer Airguns.Contents: