Kaukolastan
23-08-2005, 01:32
The Advanced Combat Rifle Project, embarked in the late 1980s, was a a US Army project to find a rifle that could deliver 100% improvement over the current M16 weapon system. This was not an attempt to field a workable weapon, but a sort of "what if" concept test. However, from this experiment come many of NS's favorite gun designs (whether the designers know it or not).
http://airbornecombatengineer.typepad.com/photos/weapons_fireams/acrcandidates467ace.jpg
Mpodels from Top: Steyr, H&K, Colt, and AAI.
The AAI – AAI loaded the standard 5.56x45mm case with a saboted fléchette. Unfortunately, while the AAI ACR's magazine was specially sized to prevent insertion of standard 5.56mm NATO cartridges, a standard cartridge could still be manually chambered in the rifle. Combined with the fléchette-tuned gas system, such a mix-up could result in a very serious mishap (kaBOOM!). As with earlier AAI fléchette rifles, users complained of the high noise levels. However, the addition of a sound moderator/muzzle brake brought the muzzle blast down nearly to the level of a standard M16A2.
The Colt ACR - This descendant of the M-16 adds few innovations, concentrating instead on improving existing designs. It does use a novel round, the Duplex Cartridge, a single round with two bullets stacked end to end. The goal of its designers was to double the performance of the old M-16 rifle. The end result is a more accurate and reliable rifle that does not differ much from its predecessor.
The Steyr ACR - The Steyr ACR was built as an attempt to revive the fleschette ammunition concept, first tried in the 1960s during US Army SPIW program. In 1960s, the fleschette concept was a failure. In 1990s, it was much more sucessful, but not enough to be worth of total rearming to the new infantry weapon system.
Steyr ACR is built around a specially designed cartridge of nominal caliber of 5.56mm. This cartridge has simple, cylindrically shaped plastic case. The fleschette, or dart, is totally enclosed in the case. Fleschette diameter is about 1.5 mm (.06 inch), lenght is about 41 mm (1.6 inch), weight 0.66 gramm (10 grains). Fleschette is partially enclosed into discarding sabot, and leaves the muzzle at impressive velocity of 1450 meters per second (4750 fps), still retaining velocity of 910 m/s (2980 fps) at the range of 600 meters. The plastic case had no rim or extracting groove, and priming compound is located annually at the inside wall of the case.
To fire such uncommon cartridge, Steyr ACR has equally uncommon design. Barrel of nominal caliber of 5.56mm, has a very slow rifling to give initial stabilisation to the fleschette, which is stabilised in flight by its own small fins. Instead of common linear-moving bolt, Steyr ACR have separate chamber (breech block), which can be moved up and down. The whole action is powered by gas drive, which has annual gas piston, located around the barrel. To understand this system i will explain how it works:
at first, lets suppose that chamber is empty and rifle is manually cocked for the first shot. In this position the chamber block is its lowest position, aligned with the topmost round in magazine. The gas piston with its operating rod is in its rearmost position and under the pressure of the return spring. When trigger is pressed, the operating rod with gas piston are released and started forward under the pressure of the return spring, which is located around the barrel. This movement, at first, via special rammer, feeds the first round forward from magazine and into the chamber, and then, via shaped cam and breech block spring, rises the breech block with the cartridge into the topmost position. In this position the fixed firing pin passes through the hole in the top of the chamber and penetrates the cartridge wall, igniting the primer composition and firing the round. When projectile (fleschette with sabot) passes the gas port, some of powder gases began to move the gas piston back. This movement, via the operating rod and shaped cam, loweres the breech block with empty case out of alignment with barrel and down to the magazine. When breech comes to stop in the lowest position, a separate rammer feeds next cartridge forward and out of magazine, chambering it. At the same time, the fired case is pushed forward out of the chamber by the next cartridge, and when cleared from the chamber, the spent case simply falls down out of the rifle via the ejection port. The ejection port is located at the bottom of the rifle, ahead of magazine, and this eliminates one of the biggest problems of any bull-pup rifle - a non-ambidextrous (or, in this case - fully ambidextrous) ejection.
If rifle is set to the full auto mode, the firing cycle is repeated as descibed above. Otherwise, the loaded breech remains in its lowest position, awaiting for the next trigger pull.
This quite comprehensive action was concealed in sleek and comfortable polymer case with AUG-styled pistol grip and large ventilated upper rib with fixed sights. Optical sights also were fitted. Due to extremely high projectile velocity, flight time was very short at any practical ranges, and trajectory was wery flat, giving the shooter almost ray-gun performance, which allowed to fire withouth prior calculations of point of impact - speaking simply, at any practical combat ranges shooter will hit where it aimed, regardless target movements (projectile flight time to the target at 300 meters is about 0.2 seconds). Due to high velocity, Steyr ACR had good killing power and armour piercing capablities, and due to the low weight of the projectile recoil was low. But it was not enough to double the M16 performance, so, for now, the Steyr ACR remains in prototype or preproductional state and the program is freezed if not abandoned at all.
The McDonnell-Douglas – WITHDRAWN FOR TECHNICAL CONCERNS
Evoking comparisons to H&R's 1962 SPIW entry, the MDHC Advanced Individual Weapon System (AIWS) used a plastic-cased, multiple fléchette cartridge. However, unlike the triangular Dardick Tround, the "Lockless" cartridge was described as a "chiclet," due to its flat, rectangular box profile. The saboted fléchette were set in the center of the box, surrounded on either side by compartments filed with propellant. The weapon's barrel was closed off at the breech end, and the chiclets are fed into the chamber through a slot through the bottom of the barrel. A pressure sleeve is then closed over the open chamber's sides before the round is fired. The spent case is then pushed out through the top of the barrel by the next cartridge as it slides into the chamber. The drawback of this system is that the amount of propellant needed is quite high, in this case nearly 3.5 times that of the 5.56mm NATO. Initial work involved duplex and triplex loadings of conventional projectiles, but due to high recoil, this was scaled back to multiplex fléchette loadings. This started with a .42 caliber five fléchette load, and was eventually whittled back to four and then three fléchette loaded in a .338 caliber sabot.
The HK G11 -The development of the G11 rifle was started in the late 1960's, when West German government decided to replace existing G3 rifle with lighter weapon with much better hit probability.
The initial studies lead to the idea of the small-caliber, rapid-fire rifle that fires caseless ammunition. To ensure sufficient stopping/killing power for small-caliber bullets used, the rifle should had have the three-round bursts capability and high capacity magazine.
The new design, called G11, was created by german company Hecler und Koch, with the Dynamit Nobel company in team. The HK was responsible for the rifle itself, while Dynamit Nobel had to develop caseless ammunition.
The rifle features unique cylinder breech/chamber system that rotates 90 degrees. The cartridges in the magazine are located above the barrel, bullets down. Prior to each shot, first cartridge is pushed down from magazine into chamber and then breech/chamber rotates 90 degrees to align the cartridge with the barrel (see pic). After that, the cartridge is fired and the breech/chamber rotates back, ready for the next cartridge to be chambered. In the case of the cartridge ignition failure, the failed cartridge is pushed down from the chamber by the next cartridge. The breech can be manually "cocked" by the rotating handle at the side of the rifle, located beyond the pistol handle. The cocking handle does not move when gun is fired. Another interesting detail is that barrel, rotating breech, feed module and magazine are mounted in the housing that can move in the rifle back and forth. When firing single shots, the housing moves back and forward after the each shot. When firing the full-auto, the housing moves back and forward during each shot, resulting in moderate rate of fire of some 600 round per minute. But, when firing the three-round bursts, second and third cartridges are feed and fired as soon as the chamber is ready for it, and third bullet leaves the barrel PRIOR to the moment when the housing becomes to its rearward position. This results in wery high rate of fire with three-shots bursts - ca. 2000 rounds per minute. Also, this results in that the actual recoil affects the rifle AFTER the last bullet in the burst is fired.
Rifle featured built-in 1X optical sight with simple circle aiming reticle. Early prototypes featured one 50 rounds polymer magazine, while latest versions featured 45 rounds magazines - one in the loaded position within the movable housing and two spare magazines on the top of the rifle, asides from the loaded magazine.
The caseless ammunition in its early appearance was designed as a block of the propellant, coated with flammable laquer, with bullet and primer "glued on" the propellant. Final ammunition design DM11, that appeared in the mid-1980s, featured "telescopic" design, when bullet was fully enclosed in the block of the propellant. The cartridge propelled the bullet that weights 3.25 gramms, to the 930-960 meters per second.
Early prototypes were prone to the ammunition cook-offs during the sustained fire, but later Dynamit Nobel solved this issue.
In the late 1980s the Bundeswehr (West German Army) began the field tests of the pre-production G11s. After the initial tests, some improvements were devised, such as removable optical sight, mounting of two spare magazines on the rifle, and bayonet/bipod mount under the muzzle.
The modified variant, called G11K2, was tested in 1989, scoring at least 50% better combat accuracy when compared to G3 rifle. Initial batch of some 1000 G11K2s was received by Bundeswehr in 1990 or so, but due to some reasons the whole programme was cancelled by German Government. Main reasons of this cancellation were, in my opinion, the lack of fundings after the re-union of the West and East Germanies, and the general NATO policy for unification of the ammunition and even magazines for the assault rifles.
G11 proved itself as a very accurate, comfortable to handle and fire, and reliable weapon.
Summary: While none of these weapons ever made it to production, the ideas within are quite impressive. Fletchette, Caseless, Duplex (and Triplex), all stemmed from this experiment. The G11 was replaced by the conventional G36 in Germany. Steyr pursued the AUG further, and the ACR fell away. AAI faded out. Colt continued to produce the M16.
The weapons of today are nothing compared to the possible weapons of yesterday, and it wasn't until the FN P90 that firearms saw any true evolution from the failed ACR Project. Today, the Russian AN94 owes its cycling action to the AAI SPIW, and the HK MP7 (the answer to the P90) derives from the old G11 PDW concept. Ironically, the old AAI SPIW project that led was resurrected as the OICW, and fell to the same concerns as before (weight, complexity), falling back into “testing” yet again.
Yet, on NS, where money is little concern, and technology rushes foreward, the guns of the ACR project seem to have a home.
http://airbornecombatengineer.typepad.com/photos/weapons_fireams/acrcandidates467ace.jpg
Mpodels from Top: Steyr, H&K, Colt, and AAI.
The AAI – AAI loaded the standard 5.56x45mm case with a saboted fléchette. Unfortunately, while the AAI ACR's magazine was specially sized to prevent insertion of standard 5.56mm NATO cartridges, a standard cartridge could still be manually chambered in the rifle. Combined with the fléchette-tuned gas system, such a mix-up could result in a very serious mishap (kaBOOM!). As with earlier AAI fléchette rifles, users complained of the high noise levels. However, the addition of a sound moderator/muzzle brake brought the muzzle blast down nearly to the level of a standard M16A2.
The Colt ACR - This descendant of the M-16 adds few innovations, concentrating instead on improving existing designs. It does use a novel round, the Duplex Cartridge, a single round with two bullets stacked end to end. The goal of its designers was to double the performance of the old M-16 rifle. The end result is a more accurate and reliable rifle that does not differ much from its predecessor.
The Steyr ACR - The Steyr ACR was built as an attempt to revive the fleschette ammunition concept, first tried in the 1960s during US Army SPIW program. In 1960s, the fleschette concept was a failure. In 1990s, it was much more sucessful, but not enough to be worth of total rearming to the new infantry weapon system.
Steyr ACR is built around a specially designed cartridge of nominal caliber of 5.56mm. This cartridge has simple, cylindrically shaped plastic case. The fleschette, or dart, is totally enclosed in the case. Fleschette diameter is about 1.5 mm (.06 inch), lenght is about 41 mm (1.6 inch), weight 0.66 gramm (10 grains). Fleschette is partially enclosed into discarding sabot, and leaves the muzzle at impressive velocity of 1450 meters per second (4750 fps), still retaining velocity of 910 m/s (2980 fps) at the range of 600 meters. The plastic case had no rim or extracting groove, and priming compound is located annually at the inside wall of the case.
To fire such uncommon cartridge, Steyr ACR has equally uncommon design. Barrel of nominal caliber of 5.56mm, has a very slow rifling to give initial stabilisation to the fleschette, which is stabilised in flight by its own small fins. Instead of common linear-moving bolt, Steyr ACR have separate chamber (breech block), which can be moved up and down. The whole action is powered by gas drive, which has annual gas piston, located around the barrel. To understand this system i will explain how it works:
at first, lets suppose that chamber is empty and rifle is manually cocked for the first shot. In this position the chamber block is its lowest position, aligned with the topmost round in magazine. The gas piston with its operating rod is in its rearmost position and under the pressure of the return spring. When trigger is pressed, the operating rod with gas piston are released and started forward under the pressure of the return spring, which is located around the barrel. This movement, at first, via special rammer, feeds the first round forward from magazine and into the chamber, and then, via shaped cam and breech block spring, rises the breech block with the cartridge into the topmost position. In this position the fixed firing pin passes through the hole in the top of the chamber and penetrates the cartridge wall, igniting the primer composition and firing the round. When projectile (fleschette with sabot) passes the gas port, some of powder gases began to move the gas piston back. This movement, via the operating rod and shaped cam, loweres the breech block with empty case out of alignment with barrel and down to the magazine. When breech comes to stop in the lowest position, a separate rammer feeds next cartridge forward and out of magazine, chambering it. At the same time, the fired case is pushed forward out of the chamber by the next cartridge, and when cleared from the chamber, the spent case simply falls down out of the rifle via the ejection port. The ejection port is located at the bottom of the rifle, ahead of magazine, and this eliminates one of the biggest problems of any bull-pup rifle - a non-ambidextrous (or, in this case - fully ambidextrous) ejection.
If rifle is set to the full auto mode, the firing cycle is repeated as descibed above. Otherwise, the loaded breech remains in its lowest position, awaiting for the next trigger pull.
This quite comprehensive action was concealed in sleek and comfortable polymer case with AUG-styled pistol grip and large ventilated upper rib with fixed sights. Optical sights also were fitted. Due to extremely high projectile velocity, flight time was very short at any practical ranges, and trajectory was wery flat, giving the shooter almost ray-gun performance, which allowed to fire withouth prior calculations of point of impact - speaking simply, at any practical combat ranges shooter will hit where it aimed, regardless target movements (projectile flight time to the target at 300 meters is about 0.2 seconds). Due to high velocity, Steyr ACR had good killing power and armour piercing capablities, and due to the low weight of the projectile recoil was low. But it was not enough to double the M16 performance, so, for now, the Steyr ACR remains in prototype or preproductional state and the program is freezed if not abandoned at all.
The McDonnell-Douglas – WITHDRAWN FOR TECHNICAL CONCERNS
Evoking comparisons to H&R's 1962 SPIW entry, the MDHC Advanced Individual Weapon System (AIWS) used a plastic-cased, multiple fléchette cartridge. However, unlike the triangular Dardick Tround, the "Lockless" cartridge was described as a "chiclet," due to its flat, rectangular box profile. The saboted fléchette were set in the center of the box, surrounded on either side by compartments filed with propellant. The weapon's barrel was closed off at the breech end, and the chiclets are fed into the chamber through a slot through the bottom of the barrel. A pressure sleeve is then closed over the open chamber's sides before the round is fired. The spent case is then pushed out through the top of the barrel by the next cartridge as it slides into the chamber. The drawback of this system is that the amount of propellant needed is quite high, in this case nearly 3.5 times that of the 5.56mm NATO. Initial work involved duplex and triplex loadings of conventional projectiles, but due to high recoil, this was scaled back to multiplex fléchette loadings. This started with a .42 caliber five fléchette load, and was eventually whittled back to four and then three fléchette loaded in a .338 caliber sabot.
The HK G11 -The development of the G11 rifle was started in the late 1960's, when West German government decided to replace existing G3 rifle with lighter weapon with much better hit probability.
The initial studies lead to the idea of the small-caliber, rapid-fire rifle that fires caseless ammunition. To ensure sufficient stopping/killing power for small-caliber bullets used, the rifle should had have the three-round bursts capability and high capacity magazine.
The new design, called G11, was created by german company Hecler und Koch, with the Dynamit Nobel company in team. The HK was responsible for the rifle itself, while Dynamit Nobel had to develop caseless ammunition.
The rifle features unique cylinder breech/chamber system that rotates 90 degrees. The cartridges in the magazine are located above the barrel, bullets down. Prior to each shot, first cartridge is pushed down from magazine into chamber and then breech/chamber rotates 90 degrees to align the cartridge with the barrel (see pic). After that, the cartridge is fired and the breech/chamber rotates back, ready for the next cartridge to be chambered. In the case of the cartridge ignition failure, the failed cartridge is pushed down from the chamber by the next cartridge. The breech can be manually "cocked" by the rotating handle at the side of the rifle, located beyond the pistol handle. The cocking handle does not move when gun is fired. Another interesting detail is that barrel, rotating breech, feed module and magazine are mounted in the housing that can move in the rifle back and forth. When firing single shots, the housing moves back and forward after the each shot. When firing the full-auto, the housing moves back and forward during each shot, resulting in moderate rate of fire of some 600 round per minute. But, when firing the three-round bursts, second and third cartridges are feed and fired as soon as the chamber is ready for it, and third bullet leaves the barrel PRIOR to the moment when the housing becomes to its rearward position. This results in wery high rate of fire with three-shots bursts - ca. 2000 rounds per minute. Also, this results in that the actual recoil affects the rifle AFTER the last bullet in the burst is fired.
Rifle featured built-in 1X optical sight with simple circle aiming reticle. Early prototypes featured one 50 rounds polymer magazine, while latest versions featured 45 rounds magazines - one in the loaded position within the movable housing and two spare magazines on the top of the rifle, asides from the loaded magazine.
The caseless ammunition in its early appearance was designed as a block of the propellant, coated with flammable laquer, with bullet and primer "glued on" the propellant. Final ammunition design DM11, that appeared in the mid-1980s, featured "telescopic" design, when bullet was fully enclosed in the block of the propellant. The cartridge propelled the bullet that weights 3.25 gramms, to the 930-960 meters per second.
Early prototypes were prone to the ammunition cook-offs during the sustained fire, but later Dynamit Nobel solved this issue.
In the late 1980s the Bundeswehr (West German Army) began the field tests of the pre-production G11s. After the initial tests, some improvements were devised, such as removable optical sight, mounting of two spare magazines on the rifle, and bayonet/bipod mount under the muzzle.
The modified variant, called G11K2, was tested in 1989, scoring at least 50% better combat accuracy when compared to G3 rifle. Initial batch of some 1000 G11K2s was received by Bundeswehr in 1990 or so, but due to some reasons the whole programme was cancelled by German Government. Main reasons of this cancellation were, in my opinion, the lack of fundings after the re-union of the West and East Germanies, and the general NATO policy for unification of the ammunition and even magazines for the assault rifles.
G11 proved itself as a very accurate, comfortable to handle and fire, and reliable weapon.
Summary: While none of these weapons ever made it to production, the ideas within are quite impressive. Fletchette, Caseless, Duplex (and Triplex), all stemmed from this experiment. The G11 was replaced by the conventional G36 in Germany. Steyr pursued the AUG further, and the ACR fell away. AAI faded out. Colt continued to produce the M16.
The weapons of today are nothing compared to the possible weapons of yesterday, and it wasn't until the FN P90 that firearms saw any true evolution from the failed ACR Project. Today, the Russian AN94 owes its cycling action to the AAI SPIW, and the HK MP7 (the answer to the P90) derives from the old G11 PDW concept. Ironically, the old AAI SPIW project that led was resurrected as the OICW, and fell to the same concerns as before (weight, complexity), falling back into “testing” yet again.
Yet, on NS, where money is little concern, and technology rushes foreward, the guns of the ACR project seem to have a home.