Adam Greig from Negative Acknowledge has developed a nice Nerf Sentry Gun, he used the NERF Vulcan which was the same gun I was thinking of using for my Nerf Gun project which is currently being finished but it was quite a bit more than the knock off that I ended up using.
Via: Hack a Day
“The gun itself is now running off a 3-cell lipo pack, which about doubles the rate of fire, and has three ammo belts chained together to give 74 rounds in one continuous burst of fire.”