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37-526: The Royal Ordnance L11A5 , officially designated Gun, 120 mm, Tank L11 , is a 120 mm L/ 55 rifled tank gun design. It was the second 120 mm calibre tank gun in service with British Army. It was the first of NATO 's 120 mm main battle tank guns which became the standard calibre for Western tanks in the later period of the Cold War . A total of 3,012 of the L11 guns were produced by 2005. The list price

74-614: A dimensionless quantity. For example, the main guns of the Iowa -class battleships can be referred to as 16"/50 caliber. They are 16   inches in diameter and the barrel is 800   inches long (16 × 50 = 800). This is also sometimes indicated using the prefix L/; so for example, the most common gun for the Panzer V tank is described as a "75 mm L/70," meaning a barrel with an internal bore of 75 mm (3.0 in), and 5,250 mm (17 ft 3 in) long. The bore to barrel length ratio

111-421: A 12/45 is 12"×45= the length of the rifled bore of that gun in inches. This explains the differences in both penetration and long range performance of various naval rifles over the years. In addition to the possible improvements in overall performance (i.e. muzzle velocity and striking force), the increase in barrel length also allowed, in some circumstances, an increase in projectile size as well. For example,

148-444: A 2,200 lb (1,000 kg) shell. The later re-design to 50 calibre not only allowed a higher velocity, but also a heavier 2,700 lb (1,200 kg) shell, which ultimately came to be accepted as the greatest naval shell ever deployed in combat . Early gun barrels were short and thick, typically no more than 26 calibers, as the gunpowder propellant they used burned very quickly and violently, and hence its acceleration time

185-475: A British Army Challenger 1 scored the longest tank-to-tank "kill" in military history, when it destroyed an Iraqi T-55 at a range of 4.7 km (2.9 miles) with an L23 "Fin" round. Since its introduction, the L11 has evolved into eight production versions. In June 1976, development of new ammunition for the L11A5 was begun. The Royal Ordnance basic L11 design was developed into a series of improved production models;

222-516: A cylindrical charge. High explosive squash head (HESH), smoke and other rounds used a hemi-cylindrical (i.e. a cylinder sliced in two lengthways) charge (the L3). Two HE charges could therefore be stowed in the same space as one AP charge. In the Chieftain and Challenger tanks, the charges were stored in 36 recesses surrounded by water jackets, so that a hit which penetrated the fighting compartment would rupture

259-533: A new 120 mm rifled tank gun in 1957. The new gun was deemed to be necessary because the British Army specified engagement ranges greater than those of other armies, for example 2,000 m (2,200 yd), as specified by the US Army, despite studies at the time that suggested engagement ranges were below those of the US Army requirements in the great majority of cases. The L11 was specifically designed to fit into

296-412: A number of ways. One common change is to use two sets of holes, each designed specifically to be efficient at capturing or releasing the gas. In this case the forward set of holes is similar to the single-hole example, but a second rearward set of holes is added, using check valves (typically ball bearings in a pit) to allow the high-pressure gases in, but not out again. The system may be arranged to allow

333-449: Is a device which removes lingering gases and airborne residues from the barrel of an armored fighting vehicle 's gun after firing, particularly in tanks and self-propelled guns . By creating a pressure differential in the barrel after the shell leaves, the bore evacuator causes most of the propellant gases and combustion residues to exit via the muzzle. Thus, when the breech opens for reloading, those gases and residues do not escape into

370-403: Is available for expanding gas from the controlled burning of the propellant charge to smoothly accelerate the projectile, bringing about a higher velocity without placing undue strain on the gun. In internal ballistics terms, if the base of a projectile is thought of as a piston propelled by the expanding gas, then as barrel length increases the volume swept by the piston also increases, and hence

407-571: Is called "caliber" in naval gunnery, but is called "length" in army artillery. Before World War II, the US Navy used 5"/51 caliber (5" L/51) as surface-to-surface guns and 5"/25 caliber (5" L/25) as surface to air guns. By the end of World War II, the dual purpose 5-inch/38-caliber gun (5" L/38) was standard naval armament against surface and air targets. All three had a bore diameter of 5   inches (not 5.51 or 5.25 or 5.38 as often misread). Naval rifles, although constructed and manufactured in roughly

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444-520: Is impossible to measure. In modern guns, increased muzzle velocities can be produced by altering powder composition and/or using duplex charges containing two different powders in order to extend the "pressure curve" further down the bore. By exposing the projectile base to a given pressure for a longer length of time, velocity can be increased without elevating the pressure level generated. Technological improvements had made it possible to introduce into use long gun barrels that are strong enough to withstand

481-597: The British to fire 120 mm APFSDS rounds, which were then in use by the Germans and Americans. The British Army argued the modifying the turret would be impractical and that a smoothbore gun could not fire HESH rounds. Polish-British tank historian Richard Ogorkiewicz argued that the later concern was unwarranted. In the mid 1980s the British Army adopted an "operational emergency" APFSDS round. During Operation Granby an L11 on

518-603: The 120 mm gun. Unlike most Western tank weapons which fire a single fixed round, the projectile and propellant are loaded separately. And unlike the Soviet 125-mm 2A46 , the propellant is in the form of a combustible bagged charge (or later, a combustible charge case for armour-piercing rounds). This required the obturation to be provided by rings in the breech rather than the cartridge case, as in fixed rounds and 125 mm separate-loaded ones. When first introduced, APDS (armour-piercing discarding sabot) rounds were fired using

555-547: The American 14/45, as introduced in the New York -class battleships, fired a 1,250 lb (570 kg) projectile. Later improvements to the design, lengthening the rifle itself and also altering the breech, allowed a 1,400 lb (640 kg) projectile and, overall, a greater barrel life. Again we see this pattern with the US 16" guns. The initial design was 45 calibers in length and fired

592-605: The L11A5 was the major production version. The breech mechanism is a downward sliding semi-automatic breechblock . The gun was equipped with a hydro-pneumatic recoil system using two buffers. The gun recoils 37 cm (15 in) in most applications. This breechblock design was based on the breechblock on the Krupp/Skoda sFH 18/43 model 18 that the British studied extensively after the Second World War and perfected for use in

629-479: The adoption of the Marconi "Improved Fire Control System" (IFCS) fitted to the Chieftain in 1979. Works cited Caliber (artillery)#Barrel length Rifled barrels introduce ambiguity to measurement of caliber. A rifled bore consists of alternating grooves and lands. The distance across the bore from groove to groove is greater than the distance from land to land. Projectiles fired from rifled barrels must be of

666-417: The amount of energy that can be extracted from the gas's burning increases. A longer barrel allows more propellant to be used: the propellant is all burned fairly early in the projectile's journey along the barrel, except in the very common instance where combustion is still occurring as the projectile leaves the muzzle and a visible muzzle "flash" is produced. The projectile continues to accelerate as long as

703-449: The barrel and a copper driving band somewhat larger than the groove-to-groove diameter to effectively seal the bore as it becomes enlarged by erosion during prolonged firing. United States Navy guns typically used rifling depth between one-half and one percent of caliber. Projectile bourrelet diameter specification was 0.015 inches (0.38 mm) less than land-to-land diameter with a minus manufacturing tolerance, so average clearance

740-402: The barrel the propellant gasses are free to flow into the reservoir. When the projectile leaves the gun the pressure in the barrel drops and the gas stored in the reservoir flows back into the barrel. By aiming these holes forward, this flow gives the propellant gasses in the barrel enough forward momentum to draw them out of the barrel. Various designs attempt to improve on the basic concept in

777-476: The breech is opened and the shell ejected as part of the recoil process. Evacuators reduce the chances of explosive propellant gases flowing backward into the turret, causing combustion as they mingle with oxygen , though this can still happen if the evacuator is poorly designed, poorly maintained, or damaged. Unprotected bore evacuators damaged by bullets have caused considerable problems in past conflicts, but up-armoring solved this problem. Bore evacuators are

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814-402: The crew compartment and pose a hazard to the gun crew. The evacuator is a passive device generally consisting of a ring of holes drilled into the barrel, surrounded by a cylindrical pressure reservoir that is sealed to the barrel's surface. When the gun is fired, high pressure gas generated by the burning propellant pushes the projectile forward. When the projectile passes the holes drilled into

851-531: The forces involved in accelerating the shell to a high velocity, while remaining light enough to be reasonably mobile, rigid enough to maintain accuracy, and having a bore able to withstand many firings before needing refurbishment. In World War I 45-caliber naval gun barrels were typical, in World War II 50- to 55-caliber barrels were common, with Germany already manufacturing tank guns of 70 calibers by 1943. Today, 60- to 70-caliber barrels are not uncommon, but

888-427: The full groove-to-groove diameter to be effectively rotated by the rifling, but the caliber has sometimes been specified as the land-to-land diameter before rifling grooves were cut. The depth of rifling grooves (and the consequent ambiguity) increases in larger calibers. Steel artillery projectiles may have a forward bourrelet section machined to a diameter slightly smaller than the original land-to-land dimension of

925-425: The gases to escape through the forward set of holes before the shell reaches it, causing a partial vacuum to develop directly behind the shell, aiding extraction. For best results, the breech must be opened at the proper time, just as the forward momentum of the gases reaches its maximum, the peak flow. This means that bore extractors are normally used only on guns with semi-automatic or fully automatic actions, where

962-440: The jacket and drench the propellant, preventing a catastrophic ammunition fire (known colloquially as a "brew-up"). The barrel of the L11A5 is fitted with a bore evacuator approximately two-thirds of the way to the muzzle and a thermal sleeve . When first introduced, a 12.7 mm (.50 in) calibre ranging gun was fitted over the barrel of the L11. The projectiles for this ballistically matched those for HESH rounds fired from

999-508: The latest technology has allowed shorter barrels of 55 calibers to attain muzzle velocities of 1,750 m/s (5,700 ft/s), as with the Rheinmetall 120 mm tank gun . However, by using discarding sabots , many such guns fire projectiles which are much smaller than the gun bore, so the relationship of projectile size to barrel length is not as straightforward as with older ordnance. Bore evacuator A bore evacuator or fume extractor

1036-411: The main armament out to 2,600 m (2,800 yd), at which point the tracer element burned out. Starting in 1971 a Barr & Stroud LF2 "Tank Laser Sight" (TLS) laser rangefinder replaced the ranging MG in British service, and in conjunction with the "Muzzle Reference System" (MRF) added in 1975, allowed engagements at ranges out to 5,000 meters. Further improvement in gunnery performance came with

1073-415: The pressure behind it is sufficient to overcome bore friction. The excess energy will continue to accelerate the projectile until it exits the muzzle. If the pressure behind the projectile drops sufficiently before the projectile exits the bore, the projectile can and will slow while still within the barrel, despite residual bore pressure behind the projectile. A light charge with insufficient pressure to expel

1110-405: The projectile will result in a "squib", or projectile lodged in the bore. This pressure is reduced by the increasing barrel volume the gas has to fill. In order to achieve maximum muzzle velocity with the shortest barrel length, the projectile should exit the barrel as the gas pressure reduces to a small fraction of the maximum, although unlike maximum chamber pressure, the small fraction desired

1147-400: The same manners as land-based artillery, were built to much more stringent and studious standards than land-based weapons, and for good reason. At sea, a weapon had to perform, without fail. There was no ready replacement, nor one that could be readily supplied. Over time, the terms of pound (weight of shell ) and bore (the actual bore of the weapon) became confused and blurred. Eventually, when

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1184-426: The technology existed, the bore (in inches or millimetres) came to be the standard measure. For naval rifles, the initial change was to actual bore, thus facilitating the manufacture of standard projectiles. They then began to measure the effective length (and therefore range) of the weapon in calibers. These are a measure of the standardized length of the barrel versus the rifled bore of the barrel. In other words,

1221-570: The turret mountings of the Chieftain tank (FV4201). After firing trials in 1961, the L11 was accepted for service on the Chieftain in 1965 and entered service with the British Army in 1966. The adoption of a rifled tank gun on the Challenger led to some controversy, and some experts later urged the British Army to retrofit the turret to fit the smoothbore Rheinmetall Rh-120 adopted by the German Leopard 2 and American M1A1 Abrams . This would allow

1258-695: Was US$ 227,000 in 1990. The L11 was developed by Britain's Royal Ordnance Factories to equip the Chieftain tank as the successor to the 105 mm L7 gun used in the Centurion tank and the heavy Conqueror tank . It was also used on the Challenger 1 , which replaced the Chieftain in British and Jordanian service. The weapon has been superseded by the L30 series 120 mm rifled tank gun. The Royal Armament Research and Development Establishment at Fort Halstead designed

1295-403: Was about 0.012 inches (0.30 mm). Driving band diameter was groove-to-groove diameter plus 0.02 inches (0.51 mm). The length of the barrel (especially for larger guns) is often quoted in multiples of the caliber, used, for example, in US naval rifles 3 in (76 mm) or larger. The effective length of the barrel (from breech to muzzle ) is divided by the barrel diameter to give

1332-434: Was needed by weight as they transformed almost entirely to gases when burned. Muzzle velocity became limited only by the length of barrel that was feasible, both in terms of the construction methods of the day and in terms of any practical constraints imposed by the gun's manner of use. The practical effect of long barrels for modern guns is that the projectile spends more time in the barrel before it exits, and hence more time

1369-513: Was short. Slower-burning " brown powder " formulations of gunpowder allowed gun barrel length to increase slightly in the 1880s, but enormous quantities of brown powder were required. New slower-burning " smokeless powder " propellants available from the mid-1880s onwards, such as Poudre B , cordite and nitrocellulose allowed a gentler prolonged acceleration, hence gun barrels were made progressively longer and thinner. The new formulations were far more powerful propellants than gunpowder and far less

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