Tracer, shell, No.13
The No.13 tracer, of steel, is cylindrical in shape and is bored internally to receive tracer compostion. The contents consist of two equal-sized pellets each of 17 grains of S.R.372 tracer compostion, making four pellets in all. On top of these pellets are pressed 12 grains of S.R.399 priming compostion.
Externally the upper end of the body is screw-threaded to screw into the recess prepared for it in the base plug of the shell, where it is retained by a set screw. The lower end of the body is screw-threaded externally to receive a metal closing cap.This cap is provided with two tommy holes, diametrically opposite, for insertion and removal of the cap, and a central hole through which the ignited gases from the tracer compostion can escape.
The central hole in the cap is closed by a thin brass disc, sweated into postion, and is for the purpose of excluding moisture. On firing, the disc is fractured by the propellant charge thus exposing the tracer compostion which is ignited.
Source: Handbook for the Ordnance, Q.F. 6-PR 7-CWT., Marks II and IV. 1943
The 6-PR 7-CWT AP projectiles were fitted with an internal tracer.