Originally Posted by Wayne02

There are two zippers, one on each side of where the buckle is fastened to the pack in the corner. One zipper is on the vertical plane and the other on the horizontal plane. When you release the buckle and pull it out/down it forces the two zippers to zip open. This opens the pack from the upper corner and presents the gun for you to grab with the strong hand. It works quite well actually as you never need to fool with the zippers individually during the draw.

Edited for further clarification: The buckle termination is sewn to the outer panel of the gun compartment thus when you pull this buckle it pulls the outer panel away, un zips the two zippers and exposes the gun.

I do wish there was some sort of holster fastened to the inside of the pack to keep the gun oriented and a little more stable.