Caldwell Picatinny AR Rifle Brass Catcher -This version from Caldwell is designed to attach directly to your flat-top AR upper receiver. It does this by using an aluminum clamp that fastens directly to the Picatinny rail. This creates an extremely sturdy brass collection device unlike your typical brass catchers that connect via Velcro straps. The Caldwell brass catcher has a generous amount of adjustability to accommodate for several rifles and optic combinations. The mesh bag features a zippered bottom and is capable of collecting approximately 100 empty .223 Rem/5.56mm NATO cases. Work with both AR-15 and AR-10 platformsConnects via Picatinny railMesh bag with zippered bottomHeat resistantCan collect 100 empty .223 Remington/5.56mm NATO cases