All 25 of the AC-130s are being converted to use 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.)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.