(May have Dark Ignition tracers.)

Over-all length, inches

Without nose fuze

Diameter of base, inches

Distance base to band, inches

Width of band, inch

Diameter at bourrelet, inch

Filling

H.E.:

Tracer:

Weight of loaded projectile, pound

Cartridge Case

Primer

Tracer

Fuzes

Nose

Length of tracer cavity, inches

Diameter of tracer cavity, inches

To eliminate the blinding flash characteristic of standard 20-mm tracers fired at night, a special Dark Ignition tracer has been developed which does not light up until about 100 yards from the gun muzzle. Rounds are designated "H.E.-T.-D.I." Over-all bruning time of this trace is four seconds; during the "dark" period there is a faint streaking in the pro-jectile's path.

The Mk 4 and Mk 7 rounds are identical except for the dimensions of the tracer cavi-ty, which is slightly greater in diameter and length in the Mk 4 than in the Mk 7. This somewhat reduces the tracer filling of the Mk 7.

The Mk 7 round is also be issued B.L. & T. with an inert filler in the H.E. cavity and a dummy nose plug. The tracer cavity contains the standard tracer mixture.

The burster charge of the 20-mm is more sensitive than the usual projectile burster charge. Accordingly, greater caution should be observed in handling.

The tracer element in these projectiles is loaded in two increments. First increament is the tracer composition, which is pressed in the after compartment by hydraulic pressure; the second increment is the "starter" mixtrue, which is pressed in on top of the tracer composition and is more sensitive than the latter. When the projectile is fired, the heat from the propellant charge ignites the starter which, in turn, sets off the tracer compo-sition.

Identification - marking and painting

Type

H.E. (Tetryl)*

H.E. (Pentolite)*

B.L. & T.

Figure 75 (Part 1). 20-mm Projectiles.