The more aerodynamic, higher velocity PGU-28A/B 20mm HEI 20mm cannon round (bottom) replaced the older M56 round long used by the F-16. It was first validated at a firing range on February 22nd, 2007, then used in battle against insurgents east of Baghdad on February 26th marking the first-ever use in battle by Air Force F-16 pilots in Iraq. [USAF photo by Capt. Ken Hall]
See also: F-16s use new 20mm ammo in battle