Spotting Rifle - Tank Main Guns

Tank Main Guns

A rare few tanks have used spotting rifles, termed a "ranging gun" for ranging their main gun. This was a short-lived use, from the period in the 1950s when the increasingly powerful tank guns (and their reduced capacity for spare ammunition) encouraged a more carefully ranged first shot in the hope of an immediate kill, and the later development of laser rangefinders.

The British Centurion Mk 5/2 with its new 105mm L7 main gun introduced a ranging gun. This was derived from the M2 Browning design, both the L6 variant of the gun and also its 12.7×99 mm ammunition. This ammunition was once again ballistically matched to the main gun. As this was a rather higher velocity round than the recoilless rifles, the case was the same as the M2 and the rounds could be used in either weapon. The enhanced tracer effect of the spotting round was sometimes used in an M2. Mounted in the Centurion it was alongside another conventional co-axial machine gun, the ranging gun being the one in the mantlet closest to the main gun.

The ranging gun was considered a success on the Centurion and was fitted to several marks of it, including retrofitting to earlier models with the 84 mm gun. The same ranging gun principle was later used for the 120mm gun of the Chieftain. It was considered less successful with the more powerful gun, as the range for accurate ranging was limited to 2,600 yards — beyond this the tracer element burned out and the fall of shot could no longer be seen. As the gun's own range with HESH could be up to 8,700 yards, this represented a serious limitation on performance. Battle planning at this time also saw a need for combat at increasing ranges, from the 2,000 yards expected for the Centurion's vintage out to 3,000 yards and beyond. As soon as they became available, the Chieftain rapidly adopted a laser rangefinder instead.

A later UK light tank using a ranging gun is the FV101 Scorpion, which uses a 7.62mm L43A1 machine gun. This is mounted as a normal co-axial machine gun and may be used as such. it is a development of the standard British L8 Tk MG, used on a number of AFVs. It has an additional barrel bearing that is used to mount the gun. This bearing, rather than mounting by the receiver as for the L8, gives a more consistent point of impact between a cold and hot barrel, which is important for use when ranging.