.50 Browning Observing
During the 1960s three marks of Observing ammunition were introduced to assist in ranging the main armament of British battle tanks. These were fired from the tank's M85 Ranging Machine gun such that when the Observing rounds struck the target and gave a smoke puff and flash the main armament was fired.
Although the word "Browning" was omitted from the nomenclature of these rounds, they were in every respect externally identical to normal Browning rounds and could be fired in any standard .50 inch Browning gun.
Prior to adoption, a number of experimental rounds were manufactured, some based on the long incendiary tracer bullet that had been developed in Britain for the American M48 Spotting Rifle cartridge. These bullets were identified usually by a red over blue or red over black bullet tip and the cartridge cases were usually unheadstamped.
Bullet weight was typically 722 grains.
The next stage was a shorter, lighter bullet of 626 grains which was to ICI Kynoch design APS.122 dated September 1959 and became ".50 inch Dark Ignition Incendiary Tracer Bullet Observing X5E1". Apart from the composition of the incendiary and tracer mix this was very similar to the service L11A1 which followed shortly afterwards.
Left: Early experimental Observation rounds using the long bullet.
L11A1
"Round .50 inch Machine Gun Observing L11A1" was approved in June 1962.
The case was the normal Browning case with a Berdan primer with a red annulus. The headstamp included "L11A1" and the round was only made by ICI Kynoch.
The bullet was boattailed with a gilding metal envelope containing a steel core bored to take the tracer composition. The tip of the bullet contained 13 grains of a barium nitrate/ magnesium composition. It was identified by two knurled rings above the case neck and a yellow over red bullet tip. Bullet weight was 626 grains
Muzzle velocity was 2,965 fps.
An inert filled bullet was produced for proof purposes with a mustard coloured tip and a purple primer annulus. There were no knurled rings on the bullet.
Left: L11A1 Right: inert filled L11A1
L11A1 headstamp
A lower pressure version of the L11A1 was produced in early 1963 and given the nomenclature "X6E1". This had a pressure of 21 tsi compared to the 24 psi pressure of the L11A1 and a slightly lower muzzle velocity of 2,900 fps. It was identified by a mauve bullet tip.
Left: X6E1
L11A2
"Round .50 inch Machine Gun Observing L11A2" was approved in June 1962. It differed only from the L11A1 by having a non-corrosive lead styphnate/ barium nitrate VH2 cap instead of the mercuric 1.7 grain cap of the L11A1. The headstamp included "L11A2".
Appearance and identification was the same as the L11A1.
L13A1
There was a requirement in the mid 1960s for a heavier tank ranging bullet to better match the trajectory of the shell of the main armament. A heavier core was required and various tungsten alloys were tried giving bullet weights in the range of 955 to 975 grains.
The design was similar in other respects to the L11A2 and in March 1968 the finalised design became the XL13E1.
In 1971 the XL13E1 was approved as the "Round .50 inch Machine Gun Observing L13A1".
The case was the normal Browning case with a Berdan primer with a red annulus. The headstamp included "L13A1" and the round was only made by ICI Kynoch.
The bullet was boattailed with a gilding metal envelope containing a tungsten alloy core bored to take the tracer composition. The tip of the bullet contained 13 grains of a barium nitrate/ magnesium composition. It was identified by two knurled rings above the case neck and a yellow over red bullet tip. Bullet weight was 965 grains
As with the L11A1, an inert filled bullet was produced for proof purposes with a mustard coloured tip. There were no knurled rings on the bullet.
Left: XL13E1. Right L13A1 with headstamps below.
