The F-35 integrated test force at Edwards AFB, Calif., started ground tests for the GAU-22/A, the internal gun for the Air Force variant of the strike fighter, according to Edwards officials. The ITF hopes to finish ground testing in August and begin airborne testing in late September. The first tests were conducted in June when aircraft AF-2 fired rounds that do not explode on impact at the Gun Harmonizing Range at Edwards. The gun uses a 25mm shell, a more powerful one than the rounds fired by legacy fighters, such as the F-16, the F-15E, and the F-15C, all of which use 20mm shells, said Maj. Andrew Rollins, the 461st Flight Test Squadron assistant director of operations. Integration of the weapon is a bit more complicated on the F-35 because it is a stealth aircraft, meaning the gun will be kept behind a retractable door until the trigger is engaged. Ground testing will help testers determine whether the door opens correctly, if the gun spins up and down as designed, and if air flow is adequate to clear gasses, states the release. The gun itself was previously tested as a standalone, and flown during test points without firing to ensure the flight envelope will not stress gun mounts. A future block upgrade to the F-35 will enable the gun’s combat operations by 2017, officials stated earlier this year.