Millet Buck Gold 4-16x 56mm Side Focus Duplex-Multi Coat Rifle Scope Heavy Duty one piece main tube provides the foundation for precise lens alignment and other components Shock-proof scopes need to absorb the heaviest recoil and field handling conditions without failure The reinforced variable power zoom ring serves to seal and support the eyepiece securely Our special sealing and purge methods for dry nitrogen fill, include internal moisture removal paths in the eyepiece Buck Gold scopes have a unique coil spring system which applies uniform pressure to the zoom assembly throughout the windage The soft mounting of lens assemblies and zoom gimble, are protected inside the heavy walled tube and elevation adjustment range The use of water resistant sealants, synthetic grease and secure O-ring seals protect against fogging over the life of the scope