February9, 2007: The U.S. Air Force has installed 30mm cannon in one of its AC-130 gunships, and is testing the new configuration for a few months before sending the first rearmed AC-130s off to war. Two years ago, the air force began work on replacing the 25mm and 40mm cannon on its AC-130 gunships, with two 30mm cannon. The Mk44 30mm Bushmaster weighs 344 pounds and fires at a rate of 200 rounds per minute (up to 4 per second). The 30mm guns used on the A-10 and AC-130 are quite different, but they use the same size ammo, and a lot of A-10 30mm ammo is being repackaged for use on AC-130s. There are still large stocks of 30mm A-10 ammo, and the AC-130 will be using more of it than the A-10.

The 30mm Bushmaster has 160 rounds available, before needing a reload. That means the gunner has 40-50 seconds worth of ammo. Each 30mm round weighs about 25 ounces (depending on type.) Explosive anti-personnel rounds are the most common round used in the Mk44. From higher altitudes (up to 20,000 feet), the AC-130 fire control system and night vision sensors, enable the 30mm gunners to accurately hit targets with the high explosive shells. The 30mm round is widely used in ground weapons as well, and there is a lot of development work going on to develop new types of ammo and fuzes. For example, the 25mm cannon did not have an airburst fuze, but the 30mm round is large enough to accommodate one (which includes a miniature radar set). This makes the 30mm ammo much more effective, as it can explode above the ground, rather than after burrowing into it. A 30mm airburst fuze is in development.

The existing 25mm and 40mm guns on the AC-130 are being phased out of military service. Actually, the 40mm gun is something of a museum piece. None have been manufactured for over a decade, and parts have to be custom made. Ammo is hard to get, and expensive, as well. The 25mm gun is no longer used by any other air force aircraft, and is being replaced on ground vehicles by 30mm cannon. The new 30mm gun is easier to operate and maintain. For example, many repairs can be made while in the air, and it's easier to reload.

All 25 of the AC-130s are being converted to use the 30mm guns. By the end of the year, there should be four AC-130s, each armed with two 30mm cannon (and a 105mm howitzer), rather than a 40mm and a 25mm cannon (and a 105mm howitzer.)