In this section I will be considering ammunition performance; essentially, ballistics. I don’t intend to consider advanced cartridge technologies such as the caseless-telescoped and plastic-cased-telescoped rounds being developed as a part of the U.S. Lightweight Small Arms Technologies programme. If one of these is eventually selected for production, it will bring the considerable benefits of a substantial weight reduction, but it won’t alter such matters as the choice of caliber, bullet weight and type, external and terminal ballistics.
To summarise a complex argument: it is both possible and desirable to develop one round which could replace both the 5.56mm and the 7.62mm in portable infantry guns. This would halve the number of different weapons and would also ensure that each weapon has a much wider range of capabilities. It would significantly reduce the weight and recoil compared with 7.62mm ammunition, while improving the range, barrier penetration and terminal effectiveness compared with 5.56mm.
If the ammunition is to be effective at long range, it must match the standard 7.62mm NATO ball round in its trajectory, retained energy and barrier penetration at 1,000 meters from the same length barrels. However, if it is to reduce the ammunition weight and recoil compared with 7.62mm, it must be smaller and less powerful. This conflict can be resolved by selecting a caliber intermediate between the 5.56mm and 7.62mm, with a low-drag bullet which will lose velocity (and therefore energy) more slowly than the 7.62mm ball. Other things being equal, low-drag bullets are heavier than usual, so to keep recoil in check need to be fired at a lower velocity. Muzzle energy will be lower than the 7.62mm (but appreciably higher than the 5.56mm) but the right specification of low-drag bullet will eventually catch up with and even surpass the 7.62mm at long range.
In practical terms, the smallest caliber likely to deliver a performance comparable with the 7.62mm is 6.5mm, while the largest which would enable recoil and weight to be kept in check is 7mm. Exactly which caliber proves to be the best compromise should be determined by more detailed analysis, comprehensive testing and preferably combat experience. Initial calculations indicate that a muzzle energy in the region of 1,800-1,900 ft/lbs will be required, compared with figures of around 1,250 ft/lbs for the 5.56mm and 2,500 ft/lbs for the 7.62mm. Experience of existing cartridges in this class indicates that the weight will be mid-way between the 5.56mm and 7.62mm, but the perceived recoil will be much closer to 5.56mm, thereby maintaining good controllability.
The U.S. Army’s ARDEC Small Caliber Munitions Technology Branch recently conducted an analysis of calibers for future infantry weapons, with the results emerging in March 2011. A wide range of criteria were examined including: penetration; terminal effectiveness; accuracy; initial, retained and striking energy; wind drift; stowed kills; and recoil. The existing 5.56mm and 7.62mm rounds were tested at various ranges in comparison with 6.5mm and 7mm, in all cases when loaded with similar lead-free bullets (copper or copper+steel – the latter representative of the M855A1). The conclusion of the study confirmed that calibers in the 6.5mm to 7.0mm range deliver the optimum characteristics for use in military small arms. This issue has since been followed up by a Joint Caliber Working Group sponsored by the TSWG Tactical Operations Support Subgroup.
The need for good long-range performance combined with a short overall length for handiness in urban fighting and in vehicles causes problems for traditional rifles, since the first requires a long barrel and the second a short one. A folding stock can resolve the carrying problem (where that is possible: which it isn’t with the M16 and M4, for instance, as the action extends into the stock) but doesn’t help in urban fighting when the stock must be extended to provide controllability.
One option is to have barrels of different lengths which can be changed depending on the circumstances, but that may not be convenient, particularly if the ranges keep changing during a patrol (for example, a section might be searching a village but then be attacked from long range as they leave). Another option is to select a compromise barrel length, but this will result in a gun which is longer than is desirable in urban fighting and which will have a reduced long-range performance – unless the power of the cartridge is increased to deliver the same performance from a shorter barrel, in which case the ammunition weight, recoil, muzzle flash and blast will be increased. The obvious solution to this dilemma is to adopt a bullpup configuration, with the action and magazine located at the back of the gun, behind the pistol grip.
The proposal of a bullpup is controversial since the U.S. Army has never used them, while the British Army has been put off them by the long and painful saga of the SA80, so requires some further justification.
There are three principal objections to a bullpup:
- Poor ergonomics: the location of the action and magazine well to the rear of the pistol grip makes operating the controls and changing magazines more difficult. This is particularly an issue with the SA80.
- Lack of ambidexterity: most bullpups (although not the SA80) can be converted to left-hand use, but that takes some time to achieve so can’t be done in the heat of battle. This means that users can’t switch shoulders to aim round the corner of a building, for instance, without being hit in the face by their own ejected cases.
- Lack of ability to adjust the stock length to allow for the wearing of body armour: again, a particular problem with the SA80 which has quite a long stock.
Apart from these practical concerns, some users dislike the rearward weight balance of the bullpup and the proximity of the action to the firer’s head in case of a chamber explosion.
There are responses to all of these objections:
- The ergonomics do not have to be as poor as the SA80’s: the latest version of the Israeli Tavor, for instance, has controls which match those of the M16 and M4 in location and operation, since it was designed to replace them.
- There are various ways of achieving ambidexterity. The FN F2000 uses a forward ejection tube, which carries the spent cases to the front of the gun before they are expelled. The new Beretta ARX-160, although not a bullpup, has a mechanism which changes the case ejection side at the flick of a switch. The STK SAR-21 from Singapore has a simpler solution for emergency left-hand use: a large and effective case deflector.
- An adjustable stock could be provided if the gun action behind the magazine were designed to be shorter: something which hasn’t happened so far since there has been no call for it. However, that should not be difficult to achieve in a new design.
Gun balance is, to a great extent, a matter of what you are used to. Some bullpup users prefer the rearwards weight balance, arguing that it is easier to hold one-handed or for extended periods, and makes the rifle quicker to change aim. What is undoubtedly true is that a bullpup is far more evenly balanced once an under-barrel grenade launcher, large electro-optical sights and other tactical kit (e.g. torches) start being added: a traditional rifle then becomes massively front-heavy.
The firer’s head can be shielded from the action by using a tough Kevlar cheek-piece, as with the STK SAR-21; this could be designed to flip quickly from one side to the other in conjunction with a switchable-side ejection system like the ARX-160’s.