The U.S. Air Force has started using a new 20mm round for its
aircraft cannon. The PGU-28A/B round has a higher velocity (because of more
propellant), and the shell has a more aerodynamic shape. This means that the
high explosive shell will explode at longer ranges. That's because, as a safety
feature, the fuze on the 20mm shell will not explode unless the shell is moving
at a minimum speed. The older, M56, round, required that the pilot fire from a
distance of about 1,000-1,500 meters away to insure that the rounds would
detonate. The new PGU-28A/B round can be fired from a distance of 2,000-2,500
meters and still go off. This gives the pilot more options when coming in, and
allows the aircraft to stay farther away from enemy ground fire.
For several years, F-16 pilots have been using a new, and much improved,
fire control system for their 20mm cannon, that has enabled them to deliver
more accurate fire at ground targets. This, in turn, as produced more calls
from ground troops for strafing runs. The pilots are glad to oblige, often to
clear snipers off the roof, or upper stories of a building. If the F-16 can't
get in close enough to have their 20mm shells detonate, the slower moving
shells are still moving fast enough to kill anyone they hit. The non-detonating
shells will also break things, and create casualty causing fragments. Moreover,
the non-detonating shells will scare the hell out of anyone in the vicinity of
impact, which will often cause enemy gunmen to depart the area before the F-16
comes back. But the 20mm shells work best when they explode.
The new round is also being used in the 20mm cannon used by some helicopter gunships, which have the same range/velocity problems as the F-16.
The air force uses a six barrel 20mm cannon, which fires at the rate of a hundred, 3.5 ounce, shells a second. F-16s carry 511 rounds. The helicopter gunships have a lower
rate of fire, and less ammo.