Biwwy is a boy in the Great Chamber of Little Lamplight. He offers to sell his unique Laser Rifle (Wazer Wifle) to you for 500 caps because he has been kicked off the scavenger team and no longer goes out on patrols -- he no longer needs a gun anymore, but figures that you might.
With sufficient Barter skill, you can haggle the price down to 250 caps. If you have the Child at Heartperk, you can get the Wazer Wifle for free. Also note that if you have a high enough Barter skill you must buy it for 250 caps, that is you can't pay what it's worth.