(By the sixthcircle)
Weapon Name- 70mm CTA Chaingun
Round Type- 70mm Cased-Telescopic
Over-all length- 6.2 meters
Barrel length- 5.28 meters
Weight- 1800 pounds
Rate of Fire- 260 RPM
Feed Mechanism- Belt fed, linkless belt
Round Capacity- 100+
Effective Range-
Range- 62,474 ft (19,042 m), 12 miles horizontally, or a maximum altitude of 43,500 ft (13,300 m), 8.25 miles
Accuracy- 1 MOA
Accessories- Picatinny rails
Quick switch firing mechanism- N/A
Scope/Sights- Picatinny rails
Muzzle Velocity- 1550 m/s (2.5 kilograms), 3 million joules - 1450 m/s (3.6 kilograms), 3.8 million joules
Firing System- Chaingun
Miscellaneous/electronic information- The weapon is essentially chaingun chambered in a 70mm high velocity cartridge, designed to take out low flying aircraft and light vehicles.
Basic Information
The weapon is a chaingun chambered in an extremely powerful 70mm cased telescopic cartridge, designed to reach extremely high altitude and long ranges, replicating or exceeding the range of the 90mm and 120mm anti-aircraft cartridges, but in a much smaller package. The goal is to provide anti-helicopter support beyond the range of most missiles employed by them, and anti-aircraft capabilities to relatively low altitude aircraft, in a package that is much lighter and smaller than would be required for larger anti-aircraft weapons, and thus suited for use in armored vehicles. The weapon functions in part as a deterrent to aircraft, forcing them to stay at higher altitudes or keep a further distance away from the vehicles, and is useful in defeating low-flying aircraft, particularly if the vehicle is at high elevation. To a limited extent it is also useful for shooting down missiles and air dropped explosives, as well as drones, capable of engaging enemy missiles as well bombs to protect infantry and other vehicles, protecting them not only from the vehicles but the weapons they use themselves (and out-ranging the cannons used on aircraft, such as the 30mm chaingun by the apache). The round has good anti-vehicle capabilities as well as anti-aircraft capabilities, designed to overmatch light APC's or infantry fighting vehicles like the Bradley. The vehicle can defeat virtually any light or medium APC, and even light tanks like the T-55 or early production T-72's, but fails to defeat the armor of main battle tanks. The rounds are still effective against tanks in many ways, capable of destroying tracks, cameras, injuring exposed crew members, destroying weapons on the vehicle including the primary gun, and in general damaging sensitive parts of the tanks that are lesser armored (such as the engine exhaust manifolds, areas where tanks must take in air). Even without total penetration of armor, it can typically perforate the outer armor of tanks, weakening it against further strikes, and necessitating often highly costly repairs given the permanent damage it can inflict, such as to underlaid ceramic chobham armor, or when detonating explosive reactive armor, commonly found in russian tanks. A study by U.S. forces found that Russian artillery was more likely to damage or kill U.S. tanks than previously expected given the periphery damage they caused, resulting in effective incapacitation even if the primary armor was not pierced. [Page 11] Given the large size of the round, it is easily used to replace mortars, and given it's high angle of fire and air-bursting capabilities, is frequently used as light artillery to support infantry. With a nearly 8 pound high explosive projectile, it is much larger than the 60mm mortar at 3 pounds, and only slightly smaller than the 10 pound 81mm mortar projectile. With it's tremendous range, it can be used alongside traditional artillery, especially when angled upwards.
The 70mm cartridge was chosen over the 90mm given it's much smaller size, with the cartridge being around 10.5 pounds, and the bullet 5-8 pounds, much lighter than the 24 pound 90mm rounds and 50 pound or greater overall cartridge size. The reduced weight and compact size, being cased telescopic, has made it easier to store a larger volume of rounds in the desired vehicle, allowing for several hundred rounds to be stored or more, designed to fit compactly inside of a larger vehicle. The cases are actually rectangular in shape, instead of cylindrical like most cartridges, to make them easier to store, similar to G11 4.73mm round, to allow more propellant to be stored in a smaller amount of space, further increasing it's carry capacity. The cases are polymer, and the round is seated within them, dramatically reducing their size and weight, to a mere 10.5 pounds. It's immense size in comparison to many smaller cartridges, such as the 25mm or 30mm chaingun rounds has necessitated these changes, but nonetheless it is far smaller than many rounds of comparative levels of power. Two main variants of the cartridge exist, high velocity discarding sabot rounds similar to tanks, with a fin stabilized dart, and a high explosive cartridge. The high explosive rounds are nearly 8 pounds (3.6 kilograms), with nearly 4 pound of filler, which can be fitted with a high explosive composition, smoke, tear gas, or chalk for marking targets. These rounds travel at a slightly lower velocity than the kinetic rounds, at 1450 m/s, designed as dual-purpose air bursting and shaped charge rounds, designed either to produce shrapnel or penetrate armor with a shaped charge jet. Larger than many RPG rockets, it's smaller diameter reduces it's penetration in comparison, as well as it's rifling spin, but 12 or more inches of penetration of RHA is possible, and fragments can be dispersed to 30-50 meters. As the shrapnel is heavy and shaped aerodynamically, like the claymore mine, it can drastically increase it's range and penetration, making it more effective against aircraft and lightly armored vehicles or soldiers. The high explosive rounds can be programmed to airburst in mid-flight, either via a laser range finder like in the XM25 grenade launcher, or due to a radar-based proximity fuse that detects the rounds distance from other objects, such as aircraft. In this way, the rounds can detonate mid-air if their trajectory is not on the path to directly intercept aircraft, causing damage to the aircraft in the event of a near miss; however, given the dual purpose nature of the cartridge, the same fuse can also be programmed to air burst in other ways, making it more versatile for use in a broader array of situations. The saboted KE round is extremely powerful, traveling at 1550 m/s, and being more capable against SLAT armor, spaced armor, and ceramic, although it's exact penetration through armor varies. The rounds however have approximately 20% of their mass taken up by the sabot, which saps much of the energy of the cartridge, but ensures their smaller dart like shape can be easily maintained. The fin stabilized rounds do not rotate in flight, which enhances their penetration capabilities to some degree. Their very high sectional density increases their aerodynamics, and they are fin stabilized, and thus they are capable of reaching an extremely long range. The rounds are traditionally made of a high strength depleted uranium alloy, like used in the M1 abrams, similar in construction to the M829 rounds, which is as capable and less expensive than tungsten.
The propellant of the ammunition was carefully chosen, designed to replicate the high velocities of anti-tank guns, with the cartridge utilizing a three-stage gunpowder which is designed to burn up in a specific, long barrel length (like in the .410 cheytac), at very high velocities, and at lower pressures. The barrel by necessity is extraordinarily long, similiar in length to the 120mm Rheinmtall cannon, given the type of propellant it utilizes, allowing for a reduced propellant load, higher velocity, and less recoil. Significant emphasis has been placed on reducing the friction and increasing accuracy of the rounds, as well as managing the heat and wear of such a high velocity cartridge, in addition to achieving the effects itself. The rounds have driving bands which match the grooves of the barrel, which is a feature often found on artillery rounds, or the 15.5mm BRG. The rounds are designed to have an extremely high BC and sectional density, and are fin stabilized, creating good aerodynamics, which increases their range and reduces disturbances in flight. The rounds utilize a high strength low friction polymer coating in replace of copper metal jackets, and exclusively are used in polygonal, gain twist barrels. The gain twist, or progressive twist reduces friction in the barrel by progressively increasing the barrel twist from the chamber, reducing the initial force upon the sudden impact of the round on the rifling on the barrel. The barrel is polygonal which also reduces friction and leaves behind little rifling marks on the cartridges, allowing them to act in part like a smoothboore barrel, thus increasing velocity. The rounds and the barrels are precision made and tested with x-rays and magnetic imaging for even minor defects, both due to the tremendously high pressure of the cartridges and the need for precision in order for the rounds to reach a long range. All of these features also have the effect of increasing accuracy and durability of the barrel, which is important to maintain accuracy at extremely long ranges. Typically, the barrels are cobalt chrome and flow formed, which has an extremely long service life and high heat resistance, making it ideal for such a high velocity cartridge. In a proof of concept test, the U.S. military fired 24,000 rounds out of an M24 machine gun in 30 minutes, at around 800 rounds a minute, a treatment that would have caused steel barrels to fail in approximately 2-3 minutes, with little degradation in accuracy. The barrels have both good heat dissipation properties and high heat tolerance, as well as low friction, making them ideal for use in this capacity. The barrel is finned, designed to help dissipate heat, especially around the chamber and throat of the barrel, which produce the most heat. The weapon also has a relatively low rate of fire, which compensates in part for it's raw power. Despite all of these features, the excessive velocity of the rounds tends to produce tremendous wear, with the weapons only having a barrel life of 8000 rounds, necessitating frequent changes with extensive use.
The chaingun is based on the Mk.44 Bushmaster chaingun, but is increased in size proportionately in order to fire the 70mm round. The chaingun is electrically automated, has a solenoid firing pin which can be recocked in the event of a light primer strike, and consumes around 10 horsepower in order to operate. Like the 40mm CT it utilizes a telescopic polymer case, but is rectangular in shape to save on size when being stored inside of a turret. The chaingun can utilize both a linkless feeding system and aluminum belt links, to improve reliability and make reloading substantially easier, particularly from other vehicles. It allows for variable volumes of ammunition with external ammunition loads, and increases reliability with linked ammunition as the linkless system assists with feeding when belts are used, serving as an assisted feeding system as opposed to a true linkless operation in this configuration. Ammunition stowage varies, but largely there is immediate access to ammunition in the turret, and stowed rounds in the bottom half of the vehicle; if the main turret is rotated to 90 degrees, it allows for reloading of the turret. The Chaingun is almost always remote controlled and unmanned, to make room for more ammunition and reduce the overall complexity of the design that is needed for manned operation. Typically three belts of ammunition are used, one for high explosive ammunition, one for armor piercing rounds, and one for smoke or other specialty rounds, with the weapon drawing from one of the three belts depending on which round is intended to be fired. Rounds are typically stored vertically, with the feeding mechanism rotating the rounds laterally before being fired. Due to the inherently large size of each of the cartridges, it is difficult to store large volumes of ammunition, however it is much greater than many vehicles like the CV90 which stores the ammunition in magazines. Given the larger size of the turret than many IFV's, and internal ammunition stowage, as well as the more densely packed arrangement of the ammunition, 200 rounds can be stored in the turret, while an additional 400 are stored within the body of the vehicle. This is quite large for virtually any chaingun, and is only facilitated by the large size of the vehicle and relatively small size of each cartridge. This has the side effect of the ammunition being more easily ignited if the armor is penetrated, but is unlikely to cause crew fatalities as they are separate internally from the ammunition and turret.
