Spotting rifle
Encyclopedia
A spotting rifle is a small-calibre rifle
used as a sighting device
for artillery
. The ballistics of the spotting rifle are matched to those of the artillery piece, so that if a shot from the spotting rifle lands on the target, it may be assumed that the main weapon will also do so.
s as anti-tank artillery, from the 1950s to the 1970s. These weapons are used for direct fire
with line-of-sight visibility to the target. As recoilless rifles have a relatively low muzzle velocity
and thus a high trajectory
, accurate ranging
is important An optical sight can measure the bearing
to a target, but not easily or accurately measure the range
. Optical rangefinder
s were too large for lightweight portable artillery, and the later development of laser rangefinders would in turn make spotting rifles obsolete.
The British BAT series
of 120 mm anti-tank recoilless rifles used a variety of sighting systems. The original BAT used a purely optical sight. The MoBAT, a lightweight and more portable version, had a 7.62mm calibre Bren light machine gun. The final version, the WOMBAT
, used the same American Remington M8C .50 in as the M40 recoilless rifle
. Both of these were used as gas-operated semi-automatic rifles. The .50 was not, as often assumed, a development of the .50 M2 machine gun
using the 12.7mm×99mm NATO
cartridge, but was a shortened 12.7mm×76mm cartridge.
Where a vehicle, such as the M50 Ontos, used multiple barrels, spotting rifles were usually provided for each barrel so that each could be accurately boresighted to its own barrel. The Ontos used six barrels with four spotting rifles; two without, to avoid making an already tall vehicle even higher. This provision may have been over-generous, although it did also increase the magazine capacity available for repeated ranging shots. Many photographs of the Ontos in service in Vietnam show it with only two of the spotting rifles installed in their mounts. The Ontos also often only carried four or even two main rifle tubes.
s.
The British 94mm LAW 80
is a rocket launcher developed as a replacement for the LAW 66
and Carl Gustav
to give a more powerful infantry anti-tank capability. This uses a 9 mm rifle with a 5 round magazine and a particularly unusual design of ballistically matched cartridge.
This same spotting rifle and round was later adopted for the US 83 mm Shoulder-launched Multipurpose Assault Weapon
(SMAW).
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 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.
Rifle
A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...
used as a sighting device
Sight (device)
A sight is a device used to assist aligning or aim weapons, surveying instruments, or other items by eye. Sights can be a simple set or system of markers that have to be aligned together as well as aligned with the target...
for artillery
Artillery
Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...
. The ballistics of the spotting rifle are matched to those of the artillery piece, so that if a shot from the spotting rifle lands on the target, it may be assumed that the main weapon will also do so.
Anti-tank recoilless rifles
Spotting rifles were most commonly used with recoilless rifleRecoilless rifle
A recoilless rifle or recoilless gun is a lightweight weapon that fires a heavier projectile than would be practical to fire from a recoiling weapon of comparable size. Technically, only devices that use a rifled barrel are recoilless rifles. Smoothbore variants are recoilless guns...
s as anti-tank artillery, from the 1950s to the 1970s. These weapons are used for direct fire
Direct fire
Direct fire refers to the launching of a projectile directly at a target on a relatively flat trajectory. The firing weapon must have a sighting device and an unobstructed line of sight to the target, which means no objects or friendly units can be between it and the target...
with line-of-sight visibility to the target. As recoilless rifles have a relatively low muzzle velocity
Muzzle velocity
Muzzle velocity is the speed a projectile has at the moment it leaves the muzzle of the gun. Muzzle velocities range from approximately to in black powder muskets , to more than in modern rifles with high-performance cartridges such as the .220 Swift and .204 Ruger, all the way to for tank guns...
and thus a high trajectory
Trajectory of a projectile
In physics, the ballistic trajectory of a projectile is the path that a thrown or launched projectile will take under the action of gravity, neglecting all other forces, such as friction from air resistance, without propulsion....
, accurate ranging
Ranging
Ranging is a process or method to determine the distance from one location or position to another location or position. Another term for this method is lateration, see unilateration...
is important An optical sight can measure the bearing
Bearing
Bearing may refer to:* Bearing , a term for direction* Bearing , a component that separates moving parts and takes a load* Bearing capacity*Bearings, album by Ronnie Montrose in 2000...
to a target, but not easily or accurately measure the range
Range of a projectile
right|thumb|250 px|The path of this projectile launched from a height y0 has a range d.In physics, assuming a flat Earth with a uniform gravity field, a projectile launched with specific initial conditions will have a predictable range. As in Trajectory of a projectile, we will use:The following...
. Optical rangefinder
Rangefinder
A rangefinder is a device that measures distance from the observer to a target, for the purposes of surveying, determining focus in photography, or accurately aiming a weapon. Some devices use active methods to measure ; others measure distance using trigonometry...
s were too large for lightweight portable artillery, and the later development of laser rangefinders would in turn make spotting rifles obsolete.
The British BAT series
L6 Wombat
The L6 Wombat, was a 120 mm calibre recoilless anti-tank rifle used by the British Army. They were used until anti-tank guided missiles such as Vigilant and MILAN took their place....
of 120 mm anti-tank recoilless rifles used a variety of sighting systems. The original BAT used a purely optical sight. The MoBAT, a lightweight and more portable version, had a 7.62mm calibre Bren light machine gun. The final version, the WOMBAT
L6 Wombat
The L6 Wombat, was a 120 mm calibre recoilless anti-tank rifle used by the British Army. They were used until anti-tank guided missiles such as Vigilant and MILAN took their place....
, used the same American Remington M8C .50 in as the M40 recoilless rifle
M40 recoilless rifle
The M40 recoilless rifle was a lightweight, portable, crew-served 105 mm weapon intended primarily as an anti-tank weapon made in the United States...
. Both of these were used as gas-operated semi-automatic rifles. The .50 was not, as often assumed, a development of the .50 M2 machine gun
M2 Machine Gun
The M2 Machine Gun, Browning .50 Caliber Machine Gun, is a heavy machine gun designed towards the end of World War I by John Browning. It is very similar in design to Browning's earlier M1919 Browning machine gun, which was chambered for the .30-06 cartridge...
using the 12.7mm×99mm NATO
.50 BMG
The .50 Browning Machine Gun or 12.7×99mm NATO is a cartridge developed for the Browning .50 caliber machine gun in the late 1910s. Entering service officially in 1921, the round is based on a greatly scaled-up .30-06 cartridge...
cartridge, but was a shortened 12.7mm×76mm cartridge.
Where a vehicle, such as the M50 Ontos, used multiple barrels, spotting rifles were usually provided for each barrel so that each could be accurately boresighted to its own barrel. The Ontos used six barrels with four spotting rifles; two without, to avoid making an already tall vehicle even higher. This provision may have been over-generous, although it did also increase the magazine capacity available for repeated ranging shots. Many photographs of the Ontos in service in Vietnam show it with only two of the spotting rifles installed in their mounts. The Ontos also often only carried four or even two main rifle tubes.
Recoilless rifles using spotting rifles
- M40 recoilless rifleM40 recoilless rifleThe M40 recoilless rifle was a lightweight, portable, crew-served 105 mm weapon intended primarily as an anti-tank weapon made in the United States...
- MoBATL6 WombatThe L6 Wombat, was a 120 mm calibre recoilless anti-tank rifle used by the British Army. They were used until anti-tank guided missiles such as Vigilant and MILAN took their place....
- WOMBATL6 WombatThe L6 Wombat, was a 120 mm calibre recoilless anti-tank rifle used by the British Army. They were used until anti-tank guided missiles such as Vigilant and MILAN took their place....
- M50 Ontos
- Type 60 Self-propelled 106 mm Recoilless GunType 60 Self-propelled 106 mm Recoilless GunThe is a light anti-tank vehicle developed by Japan in the late 1950s. It mounts two M40 106 mm recoilless rifles as its main armament.- Development :...
- FV4401 ContentiousFV4401 ContentiousFV 4401 Contentious was a prototype British air-portable tank destroyer of the early 1960s. At least one prototype was constructed and tested, although no production vehicles were built or saw service.- Project Prodigal :...
Rocket launchers
Perhaps the smallest weapons to use spotting rifles are man-portable shoulder-launched rocket launcherRocket launcher
A rocket launcher is any device that launches a rocket-propelled projectile, although the term is often used in reference to mechanisms that are portable and capable of being operated by an individual....
s.
The British 94mm LAW 80
LAW 80
The LAW 80 , sometimes erroneously referred to as LAW 94, is a man-portable, disposable anti-tank weapon currently in use by the British Army and a few other militaries.-Description:...
is a rocket launcher developed as a replacement for the LAW 66
M72 LAW
The M72 LAW is a portable one-shot 66 mm unguided anti-tank weapon, designed in the United States by Paul V. Choate, Charles B. Weeks, and Frank A. Spinale et al...
and Carl Gustav
Carl Gustav recoilless rifle
The Carl Gustav is the common name for the 84 mm man-portable reusable multi-role recoilless rifle produced by Saab Bofors Dynamics in Sweden...
to give a more powerful infantry anti-tank capability. This uses a 9 mm rifle with a 5 round magazine and a particularly unusual design of ballistically matched cartridge.
This same spotting rifle and round was later adopted for the US 83 mm Shoulder-launched Multipurpose Assault Weapon
Shoulder-Launched Multipurpose Assault Weapon
The Shoulder-Launched Multipurpose Assault Weapon is a shoulder-launched rocket weapon, based on the Israeli B-300, with the primary function of being a portable assault weapon and a secondary anti-armor rocket launcher. It was introduced to the United States armed forces in 1984...
(SMAW).
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
Centurion tank
The Centurion, introduced in 1945, was the primary British main battle tank of the post-World War II period. It was a successful tank design, with upgrades, for many decades...
with its new 105mm L7 main gun
Royal Ordnance L7
The Royal Ordnance L7 is the basic model of Britain's most successful tank gun. The L7 was a 105 mm L/52 rifled design intended for use in armoured fighting vehicles...
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 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
Royal Ordnance L11A5
The Royal Ordnance L11A5 is a 120 mm L/55 rifled tank gun design. It was the first of NATO's 120mm tank guns which became the standard calibre for Western tanks in the later period of the Cold War...
of the Chieftain
Chieftain tank
The FV 4201 Chieftain was the main battle tank of the United Kingdom during the 1960s and 1970s. It was one of the most advanced tanks of its era, and at the time of its introduction in 1966 had the most powerful main gun and heaviest armour of any tank in the world...
. 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
Tracer ammunition
Tracer ammunition are bullets that are built with a small pyrotechnic charge in their base. Ignited by the burning powder, the phosphorus tail burns very brightly, making the projectile visible to the naked eye...
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
FV101 Scorpion
The FV101 Scorpion is a British armoured reconnaissance vehicle. It was the lead vehicle and the fire support type in the Combat Vehicle Reconnaissance , CVR, family of seven armoured vehicles...
, which uses a 7.62mm
7.62×51mm NATO
The 7.62×51mm NATO is a rifle cartridge developed in the 1950s as a standard for small arms among NATO countries...
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.