By Anthony Williams
There have been relatively few attempts to introduce new heavy machine gun cartridges since the end of the Second World War. The main reason for this is that many of the roles formerly carried out by these guns have been taken over by cannon of 20mm or larger calibre, while their remaining tasks can be adequately carried out by the existing rounds. However, that has not stopped several manufacturers from experimenting, usually with new technology which possesses some theoretical advantages. The first two considered here are, however, conventional: the BRG rounds from Fabrique Nationale of Herstal, Belgium.
Having observed that armoured personnel carriers and other light AFVs were acquiring thicker armour as protection against .50/12.7mm AP rounds, FN decided to develop a more powerful HMG to give NATO an equivalent to the Russian 14.5mm KPV. The gun, designated the BRG-15, was a gasoperated, dual-feed design, and it was first chambered for a cartridge made by necking down the 20×110 Hispano case to create the 15×115. However, this experienced difficulties with barrel wear and inaccuracy, so it was decided to replace the cartridge with a new design; the 15.5x 106.
For the new BRG-15 cartridge it was decided to abandon the conventional jacketed bullet design and replace it with slightly larger-calibre projectiles using a cannonstyle separate driving (rotating) band made of plastic. It was also decided to adopt an entirely new case, this time based on theRussian 14.5×114. This is wider than the Hispano case, so it was possible to shorten it while still retaining the same ballistics, resulting in the 15.5×106. Despite all of this work, the project was shelved in 1991.
Several attempts have been made to simplify ammunition and gun design in the postwar period. These have included various shapes of caseless rounds, and “folded” cartridges with the bullet alongside the propellant. Three of the more practical efforts are described below.
.50 Dardick Tround
This system was developed by David Dardick in the 1950s, and was aimed at simplifying the gun feeding mechanism. The basic idea was to push the cartridges sideways into an open chamber instead of lengthwise into a closed one. Three of these chambers were formed on the outside of a revolving cylinder; at any given moment, one round was being loaded, the second fired and the third ejected. The cylinder was partly surrounded by a fixed sleeve; this left two chambers open for loading and ejection, but supported the round being fired by providing the third side of the chamber.
This would not have worked with a conventional cartridge case, so each round was entirely surrounded by a plastic case with three slightly rounded sides. This not only provided a close fit with the supporting chamber walls, but also added strength to make up for the lack of a solid chamber. The description “triangular round” was shortened to Tround.
Most of the initial effort was in small arms with a few examples being made for commercial sale, but these were not successful and production stopped in the 1960s. However, interest in larger-calibre automatic versions continued, mainly because the short cartridge movements involved in chambering and ejection permit a very smooth action with an extremely high rate of fire. Experiments with a .50 calibre Tround MG continued into the 1990s, but did not result in a production gun.
.50 Hughes Lockless
A different approach to the same problem was tried by Hughes in the 1970s. They also developed a gun with a sideways-loading chamber, although in this case the chamber was fixed while the surrounding sleeve moved. The ammunition was in the form of a flat box, which was slotted into the chamber from the side; the shape led it to be dubbed the “chiclet”. Before firing, the loading and ejection ports were covered by a sliding sleeve to complete the chamber. The next round to be c h a m b e r e d pushed the fired case out of the ejection port. This layout led to a very simple gun mechanism, and ammunition was made in calibres from 5.56mm to 30mm, but again without any production being achieved.
The cartridge is interesting because it is of the “telescoped” type; the propellant is packed around the bullet instead of behind it, leading to a much shorter cartridge. Ignition takes place in two stages. The primer first ignites a small quantity of propellant; just enough to drive the bullet up into the bore and thereby seal the chamber. The movement of the bullet exposes holes connecting with the main body of the propellant, which then ignites to drive the bullet from the barrel. The expansion space left by the bullet on its initial movement means thatthe propellant can be packed in tightly, allowing the case to be very compact.
.50 ARES TARG
This was another telescoped round, although with a more conventional cylindrical shape and designed for a very different type of gun action. The TARG (Telescoped Automatic Revolver Gun) was of the conventional single-barrel revolving cylinder type, as the name suggests. The cylinder had four chambers and, as with the Hughes Lockless, ejection occurred when the next round to be chambered pushed the fired case out of the chamber. The project commenced in 1989 and resulted in a light and compact machine gun, but it was cancelled in the late 1990s when ARES was acquired by the AAI Corporation.
In HMGs, as with small arms, much work on producing designs to use advanced ammunition concepts has failed to result in any production contracts. However, it seems unlikely that this will always be the case. The US Army is experimenting once more with telescoped ammunition (both plastic cased and caseless) in the Lightweight Small Arms Technologies (LSAT) programme, while the British and French are bidding to introduce 40mm cased telescoped ammunition in the CTWS (Cased Telescoped Weapon System) for future use in light armoured fighting vehicles. We have not yet reached the end of the development of the heavy machine gun cartridge.
|This article first appeared in Small Arms Review V11N5 (February 2008)|
and was posted online on October 5, 2012