(Fig. 16)

This type of tracer is used in 3.7 cm Pak and Flak H.E. shell. The tracer body of rust-proofed steel is 1.7 inches long and 0.9 inch in diameter with an external screwthread near the base for insertion in the shell. The front end is closed by a steel disc over which the rim of the body is turned. The base is closed by a celluloid disc. The filling is contai-ned in a steel inverted cup, the interior of which is lubricated with graphite. The filling consists of two pressed pellets of tracing composition and a third base pellet of tracing composition with priming composi-tion at its base. The pellets are covered with a thin even coating of graphite. Only the priming composition has a serrated finish. The priming is unusually small (a layer of about 0.04 inch deep weighing 7.7 grains) and is pressed with the lower pellet.

The three increments of tracing composition total 197.5 grains and were found by analy-sis to consist of: magnesium metal 32 per cent, magnesium hydroxide 6.2 per cent, ba-rium nitrate 36.3 per cent, barium cabonate 11 per cent, sodium oxalate 12.4 per cent and 2.1 per cent of organic matter in the form of a waxy substance.

The priming composition consists of: magnesium metal 27 per cent, barium nitrate 42 per cent, strontium nitrate 3 per cent and 28 per cent of organic matter which appears to be a phenolic resin.

The tracing composition spinning at 30,000 revolutions per minute burnt with a white light of 1,050 candle power. The estimated duration of the trace is 8 seconds.

Fig. 16