The Navy used a 20mm DU round in the ship-20 mm CIWS, though are now using the MK149 tungsten-based round; incoming sea skimmer missiles are unlikely to be heavily armored. The USMC has DU 20mm rounds for the 20mm armament of their AH-1 *Huey Cobra* helicopter gunships, though 25mm helicopter armament may replace it.
The USAF may have DU rounds for the M61 cannon aboard the F16, particularly for the F16 versions used in the CAS role. But it's far more likely they were loaded with PGU-27A/B PGU-30A TP-T *blue nose* training ammunition. Which still leaves a ¾-inch hole....
As I said, my reference point is very outdated. I hung up my spurs when DU was a relatively new thing and only used on the tank shells (The Silver Bullet) and the 30mm anti-tank stuff for the Warthog and Apache.
They've been slinging that same 20mm Vulcan cannon on AF fighters going way back to the F-104 Starfighter in the early 60s. I've heard that they have wanted to replace all of them with the 25mm for many years - but, I guess the budget hasn't found room for it?
If I was a F-16 driver with empty pylons and some 20mm rounds for the gun looking at a bad guy tank with the option of calling the 'Hogs in to work their magic, I do believe I'd call the 'Hogs (or maybe aim for the tank tracks). That 30mm is no kidding, "Get Some", tank killing ordinance!
I'm sure you're right -- that had to be TP lead slug ammo. HEI or even a tracer would have started fires?
Like So?
TM 43-0001-27
CARTRIDGE, 20MM, TARGET PRACTICE, M55A2
Type Classification: STD - AMCTC 7741.
Use: Guns, 20mm, M39, M61 and M68. The cartridge is
a training round intended as a substitute for a service
round to be used in target practice.
Description: TARGET PRACTICE Cartridge. The one piece
projectile cavity is hollow. The nose (ogive) made of
aluminum or steel is swaged to the projectile body. The
projectile is painted blue with markings in black. It
consists of a solid projectile without a fuze.
Function: The projectile is inert, therefore no specific function
takes place upon impact except penetration of the target.
Tabulated Data:
DODAC........................................ 1305-A897
UNO serial number ...................... 0339
UNO proper shipping name ; Cartridges for weapons, inert projectiles
Weight ......................................... 3935 gr
Length.......................................... 6.615 in. (168 mm)
Tracer .......................................... NA
Primer.......................................... Electric, M52A3B1
Fuze............................................. NA
Explosive:
Type ......................................... NA
Weight ...................................... NA
Incendiary:
Type ......................................... NA
Weight ...................................... NA
Propellant:
Type ......................................... WC 870 or WC 872
Weight ...................................... MBR (585 or 605 gr)
Performance: Chamber pressure........................ 60,500 psi
Velocity ........................................ 3380 fps, 78 ft from muzzle
Shipping and Storage Data:
Quantity-distance class/
SCG.......................................... 1.4C
Storage code................................ Class V
DOT shipping class ...................... C
DOT designation .......................... SMALL ARMS
AMMUNITION
Drawing number........................... 7258817
References:
SB 700-20
TM 9-1005-286-10
TM 9-1300-206 14-11