[BillyRubin]

My semi-educated hunch is that last one is a Bofors 40mm/L60 gun on an AC-130 Spectre.

For the casual audience: the US Air Force took a Hercules transport plane and stuck several guns on it, making it a gunship. That particular gun fires a 40-mm shell out of a barrel 2400mm long ("calibers" in big guns is how many times you multiply the shell diameter to get the barrel length), or about a 95" rifle barrel. The shells weigh 2 pounds apiece, leave the gun at about 2900 feet/second.) And it has a maximum firing rate of 120 rds/min, or two shots a second. The loader has to be quick.

I do not recommend ending up on the business end of this gun.

Other guns they put on the Spectre included 20mm cannons; chain guns in 20mm, 25mm, and 30mm; and also a 105-mm howitzer. (That shot shells 4" around -- almost as big as an Abrams tank shell.)

Big, scary gun. And Bofors has a great history of making really good guns.