An adaptor mount is provided for use with a gun having a Picatiny rail. A first accessory may be mounted on a first portion of the Picatiny rail of the gun. The adaptor mount has a clamp, and a mount piece having a body and a platform that, together with the clamp, defines a receiving space. The adaptor mount further includes an auxiliary Picatiny rail extending transverse to the body of the mount, with a second accessory mounted on the auxiliary Picatiny rail. A fixing screw extends through the auxiliary Picatiny rail, the body, the receiving space and the clamp, and a locking nut is positioned adjacent the clamp and engaged to the fixing screw. A second portion of the Picatiny rail of the gun is received inside the receiving space to secure the adaptor mount to the Picatiny rail of the gun.