[Drew68]

Someone correct me if I'm wrong, but I do believe that these two pictures are photos of the 20mm "Vulcan" gatling gun. Notice the magazine on the first picture!

Cheers!

[ScreamingFist]

"but I do believe that these two pictures are photos of the 20mm "Vulcan" gatling gun"

You are correct, this is the General Electric M61/A1 Vulcan cannon. The top photo also shows a 510 round ammo drum, although the ammo guide chute is not a configuration I'm familiar with.

[ScreamingFist]

After looking at your top photo in a little more detail, I belive that it is the nose mount configuration of the M61/A1 for the F-18. Also an easy way to tell the difference between the 20mm and 30mm Gatlin weapons, 20mm=6 barrels, 30mm=7 barrels. That and the 20mm looks like a pop gun compared to the 30mm, the 30mm is truly artillery.