“The Heckler & Koch HK CAWS (H&K CAWS) is a prototype automatic shotgun—designed as a combat shotgun—co-produced by Heckler & Koch and Winchester/Olin during the 1980s. It was Heckler & Koch's entry in to the U.S military's Close Assault Weapon System program.”
The CAWS (Close Assault Weapons System) is the major find of Mardin. It instantly replaces the Neostead as the combat shotgun of choice, but the minimum Strength of 6 (same requirement as the Neostead) may be beyond the average sniper. The CAWS is an unprecedented close range weapon until the next mission, when you discover the M249 SAW.
Outside of the Fallout Universe, the H&K CAWS was a recoil-operated, bullpup-configuration shotgun prototype designed to fire high-impulse shotshells using tungsten buckshot or flechettes with an effective range of 100-150 meters and a 10 round box magazine. It had a fire selector switch similar to the G11, with a full-automatic firing rate of approx. 240 rounds per minute. It never reached production due to the cancellation of the CAWS project by the US.