The AR15 is a popular rifle platform, but with a longer scope, like the Viper PST Gen2, you need the scope to lean forward more than your receiver allows. That is the design principle behind the extended cantilever scope mount from Vortex. With a center height of 1.435", the mount will support most scopes with an objective lens (bell) of 50mm and smaller.
Ensure a proper position, clearance, and height for you scope with the Vortex Viper Extended Cantilever Mount. This mount fits 34mm main tubes and will provide forward placement for your optic while holding the line of sight slightly lower than average at 1.435" above the base. Constructed of anodized lightweight but strong aluminum. Designed for the Viper, applicable for many 34mm scopes.
Vortex
LaRue Tactical