By Kevin Dockery
In the post-WWII years, the problem of increasing the range of a grenade, while increasing the accuracy and cutting back on the weapon weight, was studied more closely. At the height of the Korean War in 1952 the project received a priority push to develop both the ammunition and a new weapon to launch it. Several different avenues of approach were taken simultaneously by the military ordnance community to develop the new weapons system.
The US Army Ballistic Research Laboratories (BRL) at Aberdeen Proving Grounds had established by 1951 that a small explosive package could be made that delivered controlled fragmentation that would be effective within a limited radius. By using small fragments that could be consistently produced in a grenade-type munition, the BRL came up with the parameters that the new round should be designed to fit.
Picatinny Arsenal in Dover, N.J, became the central controller for the development of the new round of ammunition. The most effective caliber was determined to be 40mm to fit the BRL guidelines. Initial designs to control the fragmentation of the grenade centered on using a hollow-walled projectile with the space filled with small ball bearings. This idea was soon dropped when it was determined that an excessively large number of ball bearings would be needed to match the estimated production quantities of ammunition desired by the army.
Fragmentation for the new round would be accomplished by internally segmenting the grenade body so that it would break up according to established lines. The Stanford Research Institute came up with an efficient way of making engraved sheet stock that could be formed into a spherical grenade body that would produce fragmentation very close to that of the ball bearing design. the engraving process, called “roll coining”, made a sheet of steel that could be formed into a ball and filled with high explosive. When detonated, the steel body would break up along the engraved lines creating hundreds of small, 2-grain (0.13 gram), square fragments. The fragments would be traveling at an initial velocity of up to 5,000 feet per second from the point of detonation. But the low weight of the fragments, combined with their poor aerodynamic shape, caused them to lose velocity quickly. This gave the new grenade a casualty radius of only five meters.
The Chamberlain Manufacturing Corporation came up with an even simpler and lower-cost version of the grenade body. The Chamberlain fragmentation body was formed from rectangular steel wire, 1/8 inch wide by 1/12 inch thick and notched every 1/8 inch along its length, copper-brazed together into the form of a ball. This wire ball would form the same quantity, size, and type of fragments as the coined steel Stanford version, giving the design the same casualty producing radius.
Working with outside companies such as Honeywell Incorporated, Picatinny came up with a fuze system for the new grenade that was considered a marvel of miniaturization at the time. Even with the small size of the fuze, it was as large as the fragmentation body itself and made up over 50% of the complete projectile. Further studies of the new projectile centered on determining which would be the best way to launch and stabilize it in flight.
Colonel Rene R. Stutler, Chief of Small Arms Research and Development for US Army Ordnance, at his office in the Pentagon had decided that a shoulder fired launcher dedicated to launching the new grenade would be the way the project would go forward. A deputy to Colonel Stutler, Jack Bird, became interested in the grenade launcher project and investigated the idea on his own time.
Taking a piece of pipe that would accept a golf ball, Bird capped off one end and drilled several small holes through the tube’s side. With a spring placed in the tube and a golf ball dropped down over the spring, a stick was used to push the ball down against the pressure of the spring. A nail slipped through one of the holes in the side of the tube held the ball in place on the compressed spring.
Demonstrations of Bird’s “launcher” took place in the central courtyard of the Pentagon. The high arcing trajectory of the golf ball when the cross nail was pulled out demonstrated remarkable accuracy for such a crude device. The high lobbing arc of the ball reminded a number of the onlookers of a nine-iron stroke on a golf course. Jack Bird suggested the program for the new weapon be named after the popular term for a nine-iron at the time, a Niblick. Stutler agreed and Project Niblick was so named.
Once the basic projectile had been established, both a launcher and a means of propelling the grenade were needed. Springfield Armory received funds in June 1952 for its Research and Development Division to conduct a study of various devices to launch the new grenade design. A number of designs were established, built, and tested at Springfield Armory using the various forms of ammunition, now known as the Niblick projectile, coming from Picatinny.
Launchers for the Niblick projectile at Springfield Armory from 1952 into 1955 concentrated on muzzle attachments for the M1 Garand service rifle. These launchers used a blank cartridge to propel a Niblick projectile much like a standard rifle grenade. Designs ranged from a simple tube to a complex 8-round semiautomatic launcher attachment that had a circular magazine holding the projectiles. None of the designs had much advantage over the standard rifle grenade and did not show enough promise for further development.
The Niblick projectile used in most of the muzzle launcher attachments was a drag-stabilized round with an extending skirt that spread out behind the fired projectile. A spin-stabilized Niblick projectile, resembling a fat bullet, was found to have much more promise in terms of accuracy. A cartridge design with a self-contained propellant was needed to further develop the potential of the Niblick projectile.
To fire the very large Niblick projectile from a cartridge case, the standard method of simply filling the case with propellant would not fit the needs of the project. When a standard small arms cartridge is fired, the projectile receives a very violent push from the rapidly burning propellant that gradually lowers in pressure as the projectile moves up the barrel. Using the standard cartridge system with the Niblick projectile would create several recoil problems, eliminating the possibility of a shoulder-launched weapon. Lowering the velocity of the Niblick projectile to allow a shoulder-fired weapon would cause most propellant powders to burn erratically at best, ruining accuracy from round to round, and badly cut back on the effective range of such a system.
During World War II, the Germans had faced a similar question, but for different reasons. The German question was how to build a worthwhile antitank weapon that would be lightweight, use few critical materials, and still have range, accuracy, and lethality. The use of a rocket projectile was ruled out due to an inherent lack of accuracy at long range and a very high consumption of fuel when compared to projectile weight.
A new internal ballistics principle, the “Niederdruck” or high-low pressure system was developed in Germany during WWII and was used by Rheinmetall-Borsig to solve the antitank weapon question. In the high-low pressure system, a relatively small amount of propellant is burned in a high pressure chamber until it reaches a threshold pressure and ruptures a seal. With the seal ruptured, propellant gases bleed through small holes in a metal plate into the low pressure chamber where they bear on the projectile. When fired, pressures in the high pressure chamber reach the 30-40,000 psi range while the low pressure chamber maintains a reasonably steady 3,000 psi. The high pressure chamber allows the propellant to burn completely and efficiently. The low pressure chamber gives the projectile a steady push with the pressure curve having a flat, almost optimal, line.
The steady push of the low pressure portion of the high-low system gives a useful velocity to the projectile but also allows for a more fragile projectile to be used than that of a regular cannon. The low pressure also gives a low recoil impulse but is very consistent for accuracy. The major stress of firing is in the high-pressure chamber so the barrel and resulting support equipment for the weapon can be made much lighter.
The German weapon that fielded the high-low pressure system was the Rheinmetall 8cm Panzerabwehrwerfer 600, or PAW 600. The PAW 600 fired a fin-stabilized, hollow-charge round that would penetrate 5.5 inches (14 cm) of steel, out to an effective range of 600 meters. the smoothbore weapon had a light barrel with only the breech section requiring heavy walls to withstand firing. Set up for action the PAW 600 only weighed some 1,389 pounds (630 kilograms) while a conventional 5-cm Pak 38 cannon weighed 2,205 pounds (1000 kilograms) and only had some 400 meters additional range with much less penetration.
Though considered revolutionary in concept and the only major ballistics advance of the war, the high-low pressure principle was not developed further in the years following World War II. In the 1952-53 time period, Picatinny Arsenal revived the high-low pressure system to propel the Niblick projectile in a self-contained round of ammunition.
The high-low pressure cartridge case was made of aluminum and was unique in its design. The center of the cartridge case was the high pressure chamber, a thick walled extrusion in the center base of the case. Spaced around the side of the high pressure chamber are six precise vent holes. The inside of the high pressure chamber is sealed with a thin brass cup that contains the powder charge and closes off the vent holes. The bottom of the cartridge is closed off with a thick base plug that holds a percussion primer.
When the 330 milligram (5 grain) propellant charge of M9 smokeless powder is ignited by the percussion primer, it builds up a pressure of 35,000 psi while burning. When the 35,000 psi point is reached in the high pressure chamber, the brass seal ruptures and the propellant gases bleed out into the low pressure chamber where they are reduced to a pressure of 3,000 psi. The 3,000 psi pressure moves the projectile up the barrel at a relatively slow rate, maintaining close to full pressure throughout a 14-inch barrel length. The Niblick projectile left a 14-inch barrel with a muzzle velocity of 250 feet per second and a right-hand spin of 3,700 rpm due to the rifled barrel.
The self-contained Niblick round kept a relatively low bore pressure in the launchers when compared to standard ammunition. The only point of high pressure stress when firing the round was taken up by the high-pressure chamber itself. These facts allowed the barrels of the various Project Niblick launchers to be made of aluminum. The low muzzle velocity also prevented any of the launchers from having excessive recoil even though a very large and heavy projectile was being launched for a hand-held weapon.
A number of launchers for Project Niblick were produced at Springfield Armory in 1953 under the direction of the project director, Cyril Moore. Two specific designs of launchers for the Niblick round showed considerable promise. One device was a simple shotgun-like fixture for determining ballistic data for the complete Niblick round. The other launcher was designed to fire six rounds semiautomatically. This was the first of the Project Niblick weapons that was a dedicated, shoulder-fired system. With a large rotating cylinder, the device acted much like a shoulder-fired revolver. Though the idea of semiautomatic fire held promise, the first device was found to be unsuitable for military use.
In the 1954-55 time period, the focus at Springfield Armory was on utilizing the complete Niblick round, though there was still some experimentation with the earlier types of projectiles. At this time, the S-3 launcher, a single-shot, break open, shoulder fired device with a rifled barrel was produced. This device greatly resembled the Federal Laboratories tear gas gun that was popular with police departments at the time but with a more complex sight and a forward hand grip.
A more complicated launcher that had semiautomatic capability was developed and under study by 1955. Identified as the S-6 strip-type shotgun, this was the first weapon to use a semiautomatic capability built into a conventional shotgun format. The S-6 used a harmonica-like strip of three Niblick rounds, each held in its own firing chamber, and feeding through the side of the receiver to give a semiautomatic fire capability. As each round was fired, a spring would drive the strip clip through the receiver until it indexed on the next loaded chamber. This form of launcher met with high approval in the conferences between Springfield Armory and Army Ordnance personnel and effort was put into refining the design.
A second generation semiautomatic S-6 launcher was available within a few months of the first model being accepted for development. Shortcomings from the first S-6 were eliminated in the second generation design. Further work was needed to meet the military needs of such a weapon system and study continued on the design. Other launchers were examined, including large flare-gun like pistols, to use the Niblick round, but none of the designs met with much success.
Later in 1955, the experimental Project Niblick weapons were due to be tested by the Army Infantry Board. Lieutenant Colonel Roy E. Rayle, the Small Arms R&D Chief at Springfield Armory, suggested further development go into another single shot launcher like the earlier S-3 design. Instead of developing a new design, Rayle suggested an already existing pattern, such as the Stevens Model 220 hammerless shotgun with a top-mounted safety and release lever, be modified to fire the Niblick round. The advantages of such a design would be the simplicity of operation and ease of training to recruits.
Lieutenant Colonel Rayle’s suggestion was followed and a second launcher was developed along the lines of the S-3, this one identified as the S-5 shotgun. The S-5 was the first attempt to build a Niblick launcher that followed the lines of a conventional, single-shot, sporting shotgun. The lines of the S-5 remained simple and the mechanism straightforward. Further development continued on the design especially on the shoulder stock and sight configurations. An immediate drawback to the S-5 that limited its appeal to the Army personnel was that the system was single-shot only.
During testing, the S-6 repeating grenade launcher was found to have problems with accuracy and was considered awkward to handle and operate. These problems were quickly traced to the harmonica magazine. A lack of a positive seal between the mouth of the magazine and the rear of the barrel caused propellant gases to slip though the gap. This caused irregular muzzle velocity in the S-6 weapon and greatly limited the firing accuracy of the system. The much simpler S-5 launcher was favored by the Infantry Board testers. A decision was made to try and correct the problems with the S-6 launcher in order to retain the semiautomatic capability while retaining the S-5 design in reserve.
By 1958, the S-6 design had evolved into the T148E1 and T148E2 launchers. The T148E2 design was more complicated than the E1 as it incorporated a break-open design to help seal off the barrel/magazine gap. The greater number of components in the T148E2 design eliminated it from further development in favor of the simpler T148E1 pattern. A limited pilot-line production of 200 T148E1 launchers was conducted between 1 January and 30 June 1958 to supply a number of the weapons for field testing and further evaluation. The gas bleed-off at the chamber/barrel gap still caused an unacceptable loss of accuracy and the T148 project was terminated after 1 July 1960.
A conference of Army and Springfield Armory personnel decided the S-5 design, now known as the XM79, should be reactivated. US Army Infantry Board testing determined that a new sighting system should be designed and a few shortcomings of the XM79 be corrected before acceptance. The new sight design was ready by October 1959 and all XM79 launchers produced up to that point refitted with the correction. On 15 December, 1960, the M79 was officially type-classified and adopted by the US Army. Further production difficulties in producing the complicated rear sight limited weapon availability for some years after adoption.
By 1965, the M79 grenade launcher was in full production and available for issue to all of the services.
|This article first appeared in Small Arms Review V5N8 (May 2002)|