Shoulder Fired Arms – Requirement and Technologies

The Sig Sauer XM-5
The Sig Sauer XM-5 was selected by the US Army as the infantryman weapon under its NGSW programme. It uses the new high velocity 6.8x51mm Sig Hybrid .277 round which reflects a possible return to the Battle Rifle using longer-range full-scale ammunition. (Sig Sauer)

Shoulder fired weapons are not only the mainstay of the infantryman but also a vital complement for other combat and support personnel.

Shoulder fired weapons are the infantry squad’s primary means of influencing combat by either directly engaging targets or suppressing an area to allow another element to manoeuvre, while other soldiers not directly in the front line may more often have the weapon for self-protection. These weapons may differ according to the differing needs of users, their environments and roles. Adding to the design challenges are often competing requirements for automatic firing capability, weight/length preferences, various effective ranges, accuracy, ammunition performance, and logistics considerations. How these factors are addressed is often resolved by applying a mix of combat lessons, technologies, and traditions.

Rifles and Carbines

‘Long arms’ usually fall into two categories – the service rifle and the carbine. The former are longer and employed by infantry, while the later are shorter. Initially used by horse cavalry and cannoneers, the carbine became the weapon for non-infantry soldiers and special units. Service rifles with a longer barrel typically use larger calibre ammunition and have greater effective ranges and target effect. The carbine’s shorter barrel offers less opportunity for propellent burn and less powerful cartridges which result in decreased range and stopping power. For example, both the .30-06 M1 Grand of World War II and 1960s 7.62mm M14 used essentially the same size ammunition as their bolt action Great War predecessor the 1903 Springfield. Being lighter and more compact, carbines are easier to handle, but the rifle’s length and mass can provide a more stable platform. This also offers an advantage when employing a bayonet which for many decades was a major combat consideration.

Weapon Characteristics

For an individual weapon, physical aspects such as weight, length, and ease of operation are important factors. A lighter weapon is easier to carry and less fatiguing for the infantryman, while a shorter length barrel can be quicker to handle in dense vegetation, close-quarters, and urban combat. On the other hand, these factors need to be balanced against weapon performance. Longer effective range typically means a longer barrel. Similarly, target penetration and lethality may require a larger calibre bullet, which may drive the weapon’s weight particularly for accurate automatic fire. The reality is that many desirable characteristics for the shoulder fired weapon are competing, meaning choices must often be made between them.

An army’s appreciation of its anticipated battlefield, threats to be encountered and tactics required, drive weapon choice and dictate which trade-offs are acceptable. Weapons manufacturers respond to these requirements by tailoring experiences and existing technologies to best meet these needs. A case in point, despite post-war combat analysis indicating typical engagements were around 200m and rarely exceeded 300m, the US and Western armies standardised NATO full size 7.62x51mm for its small arms which could effectively engage targets at ranges to and beyond 500m. While the longer range capability was also well suited to machine guns, it also meant the infantryman would carry a much heavier ‘battle rifle’ and less ammunition. The Soviets, drawing on different lessons, fielded the AK-47/AKM built around an intermediate calibre 7.62x39mm which had a 350m range but was lighter and allowed soldiers to carry more ammunition. The trade-offs on even seemingly simple features such as a magazine capacity of 20 or 30 rounds can have significant impact on a weapon’s combat employment.


Since the introduction of magazine fed shoulder fired weapons the typical configuration has largely mimicked earlier clip-fed, semi-automatic and bolt action rifles. These see the trigger placed behind the receiver and magazine. A stock or chassis is added so that the weapon can be shouldered. This layout drives the overall length, complicating the drive for a shorter weapon while maintaining barrel length in order to preserve the performance benefits. The design of folding butt stocks is directly associated with the desire to shorten the weapon. This traditional configuration is more compatible with the larger 7-8mm standard calibres common up until 1980, and is used in most service and battle rifles including the M14, FN Herstal FAL, Heckler & Koch G3 (Gewehr 3), and others. This configuration continued to be the rule despite the move to intermediate calibres like the NATO 5.56mm and Russian 5.45mm as used in the US M16/AR15, Soviet AK-47/74, Chinese QBZ-95 and others. It also has the advantage of its layout being familiar to soldiers since the majority of military shoulder fired weapons today use this configuration.

An alternative configuration is the Bullpup which locates the receiver within the rifle-chassis placing the trigger forward of the magazine. This approach allows a 8-10in (200-250mm) shorter weapon length while maintaining the full barrel. It also equally distributes the loaded weight offering the shooter both a balanced feel and more stability in rapid firing. The addition of accessories like laser pointers, flashlights and particularly suppressors can be accommodated in the Bullpup design, without shifting weight forward. This results in the Bullpup being easier to manoeuvre. The Bullpup does have a radius using iron sights, although this is not a factor using an optic sight. Possibly the principal adjustment for the soldier is getting used to the different magazine position. The first widely fielded Bullpup was the French FAMAS in 5.56mm calibre. The British Army adopted the SA80 which was transformed into the L85 and subsequently improved by H&K as the L85A5. Likely the best known Bullpup is the Steyr AUG which has evolved to the A3 version as well as the latest Australian Lithgow produced F90 (officially the F88 Enhanced). In addition, the Peoples Liberation Army (PLA) Bullpup, the QBZ-95 in 5.8x42mm was fielded as a family of weapons. Another widely fielded Bullpup is the Tavor TAR-21 by Israel Military Industries which was adopted as the X95 by the Israeli Army over the M4A1. It has subsequently been purchased and in use with over 30 militaries including the Thai Army. In addition, PT Repubilik Armament in November debuted its IFAR22, a Bullpup design for the Indonesian Future Assault Rifle.

EF-88 Bullpup
Australia selected the EF-88 Bullpup over the M16 as its standard issue carbine. Even with a 16 inch (407mm) barrel, its Bullpup design offers a total length of only 28in (701mm) with a weight of 7.15lbs 3.25kg) making it ideally suited for close quarters, urban, and mounted troop use. (AuMoD)

Rugged and Reliable

With a strict focus on its user audience Mikhail Kalashnikov designed the AK-47 as a weapon that could be reliably operated by just about anyone. Though its manufacture was less than refined it was rugged and required minimum care. It becoming one of the most widely used individual assault rifles. The design, using 7.62x39mm, reflected the assessment that typical riflemen engagements occurred inside 300m with the ability to deliver more shots perceived as more important than accuracy at longer ranges. This relatively simplistic philosophy was carried over by Kalashnikov in the AK-74 following the shift to smaller calibre/ higher velocity ammunition which began with the introduction of the US 5.56x45mm. This change allowed a weapon weight reduction and its lower recoil made it easier to handle, while providing increased 500m effective range while maintaining the 30 round capacity magazine.

Small Arms Families

The idea of having a common weapon design that would fill many shoulder fired weapon roles has definite benefits, particularly where employed by combat teams. The Eugene Stoner 63A introduced in the mid-1960s achieved this design objective using a common receiver which was reconfigurable to six specific versions. These included a magazine feed combat rifle, carbine, and automatic rifle and belt-feed light, medium, and fixed machine guns. Remarkably, the 63A are also very lightweight with the light machine gun only 11.7lbs (5.32kg). Although well received in combat evaluation and actually fielded by the US Navy SEALS, it was not widely adopted. The principal concern being that it might be beyond the capability of the average soldier. However, this modular weapon encouraged other designers.

Providing a family of shoulder-fire weapons offers some of the benefits of a comprehensive modular design, but limits the adaptations directly to the individual soldiers’ roles. One approach is designing a weapon that can fill multiple individual applications by providing different lengths and weight. The Heckler & Koch HK416, which has been adopted by 27 militaries including Norway, the French Army and US Marines, offers this. Its family character is in its multiple barrel lengths of 10.4 in (264mm) sub-compact, 14.5in (368mm) carbine, 16.5in (419mm) rifle, and 20in (508mm) full-size. The muzzle velocity increases with each length increasing its effective range from the subcompacts 300m to 800m for the full-size rifle. The price for greater range is more weight with the sub-compact at 8.2lbs (3.7kg) increasing to 8.8lbs (4kg) in the carbine.

HK416 assault rifle
The US Marines joined France and Norway in adopting the Heckler & Koch HK416 assault rifle as their standard long arm. This meant that each Marine armed with the M27 (their designation) had the capability to serve as an automatic rifleman. (USMC)

Poland’s FB RADOM MSBS GROT is designed as a modular individual weapon that can be configured as a standard or Bullpup assault rifle, a carbine, a squad automatic rifle (with a heavier barrel), and marksman rifle. Its modularity allows field reconfiguration, changing the barrel between the 10in and 16 inch and either a MSBS standard or AR carbine stock. It can also adapt for either right or left-handed shooters. Company spokesperson, Krzysztof Kozieł, shared that the GROT design is further able to provide in 5.56mm NATO, 7.62x39mm, or other rounds based on user and applications.

The FN SCAR provides a common weapon that can be provided in either 5.56x45mm NATO or 7.62x61mm, referred to as the SCAR-L (Light) and SCAR-H (Heavy). Each of these are further offered in Close Quarters Combat (CQC), Standard (STD), and Long Barrel (LB) versions. Each version has a high degree of commonality. The rifle is adaptable with FN even introducing a sniper version the SCAR 20 SSR (Sniper Support Rifle) with 20in barrel. User reviews suggest that SCAR is easily handled (the folding stock is much appreciated), has low shooter recoil, is light and accurate. The calibre versatility may contribute to its wide use by special units.

Infantry/Squad Automatic Weapons

Since the 1940s the squad has typically comprised riflemen and members with an automatic fire weapon. In practice these two roles have been filled most often by different weapons, still the idea of a common design to fill both roles has attraction. An attempt to provide an automatic rifle (AR) version of the M14 rifle proved unsuccessful due to inaccuracy and overheating in full-auto firing and its low 20 round magazine capacity. The US Marines in 2011 adopted the M27 (based on the H&K HK41) as its Infantry Automatic Rifle (IAR) replacing the belt-fed M249 Squad Automatic Weapon (SAW) . SAW has higher light machine gun (LMG) rate of fire but with an 12 MOA of less accuracy than the magazine feed IAR’s 2 MOA. Field experience suggested that IAR’s more precise shot placement could offer equivalent suppression to an LMG. It was also much lighter at 4kg (9 lb) vs 10 kg (22lb) and could be used in close and urban combat. The Corps 2018 decision to field the M27 to every combat squad member fulfilled the idea of a common individual squad weapon.

The US Army chose its own path toward this goal. Its Next Generation Squad Weapon combines a new weapon with the introduction of a new 6.8mm calibre – the objective being to replace the current 5.56mm, M4 and M249. Following a competition Sig Sauer’s adaptation of its MCX SPEAR was selected and designated XM5 as the combat rifle and MMG to the XM250 automatic weapon. The XM250 is a belt-fed light machine gun style weapon that is lighter than the M249 at 13lbs (5.9kg) without a suppressor. Although a LMG, the XM250 does not have a quick-change barrel (like the M249) which addresses barrel overheating with sustained fires.

The XM5, which the Army will issue only to forward fighters, is heavier than the M4 and uses a 20 round magazine. Mark Cochiolo, a retired Navy SEAL, in an online review observed: “where the M4 is an assault rifle using an intermediate ammo, the XM5 is a return to the Battle Rifle with heavier and ‘hotter’ rounds (much like the M14). The result is a rifle that is heavier at 9.78lbs (4.4kg) with 20 rounds than the M4 Carbine with 30 rounds at 7.75lbs (3.52kg), which it is replacing. However, the XM5’s 6.8mm has greater effective range and is intended to penetrate body armour at 500m using the Sig Sauer proprietary hybrid case ammunition. Initial unit low scale fielding of the new weapons is expected in late 2023.

Personal Defence Weapons

A relatively recent weapon class is the Personal Défense Weapon (PDW). It resulted largely from the concern at the time that soldiers in support and logistics roles which were primarily equipped with pistol calibre hand arms would be unable to effectively engage body armour outfitted opponents (like paratroopers). A NATO 1989 requirement seeking an easily handled more compact weapon with effective range around 200 meters that could penetrate Level III body armour. The last influenced the consideration of smaller calibre higher velocity ammunition. FN’s P90 at 5.7x28mm in a 19.9in (505 mm) with a uniquely shaped 50 round top magazine weapon was the first designed and offered in 1990. It was followed in 2001 by the H&K MP7A1 at 4.6x30mm with 16.3in (415mm) minimal length but with a collapsible stock in a more traditional design. Both successfully met the requirements, including armour defeat. However, a reduced concern of supporting soldiers facing body armoured threats saw special operators more attracted to the P90 and MP7A1 rather than the original intended pistol users. This also saw the introduction of pistol (example the H&K MP5K) and other calibres including 5.56mm NATO by a variety of manufacturers in PDWs. The US SOCOM contracted in May 2022 with SIG Sauer for its Rattler.300 Blackout round. Their rationale mirrors the current application of most PDWs today, which is “providing a more portable weapon that a rifle or carbine with more power than a pistol for use in close-quarters”.

The FN P90
The FN P90 was originally intended as a personal defence weapon for vehicle and artillery crew to provide effective fires against body armour equipped enemies. It uses a Bullpup design and top 50 round horizontal magazines to remain compact 20in (500mm). It is 5.7×28 mm calibre with an effective range of 200m. (FN)


Weapons and ammunition are tightly intertwined. The characteristics of each combined with the skill of the shooter dictate the performance in an engagement. Variations in bullet size (calibre), propellent types, and case design can significantly alter recoil levels, trajectory, range, penetration, target effect, accuracy and round weight. This directly impacts on the performance of the round. For example, as suggested earlier the “full size” 7.62mm NATO Ball will reach out further and penetrate foliage without altering the bullet path. It, however, is heavier meaning less rounds can be carried, requires a heavier weapon, and has more recoil. The 5.56mm NATO uses a lighter, faster bullet with less recoil offering more comfortable firing and a lighter weapon with the ability to carry more ammunition. It, however, can be more easily deflected, less range and lower penetration.

Accuracy, range and, to a degree penetration can be addressed by higher velocity and through the bullet composition. The later includes bullets with a  hardened steel, tungsten, or tungsten carbide cure penetrator. Examples include the 5.56 SS109 and M955 or 7.62 M993. Higher velocities can be achieved with a longer barrel allowing propellent to burn longer or/and use of more or “hotter” propellent. An example of the former is shown in the muzzle velocity of the M4 Carbine with M193 round is 2,986 ft/s (910m/s) with a 14.5 inch barrel but drops to around 2600 ft/s (792m/s) in the 10.3 inch Close Quarter Battle version.

An obstacle to substantial velocity increases through propellent changes has been limited by the use of brass casings which if used can fail. This has been overcome by at least two new technologies. Sig Sauer explained it has introduced a hybrid steel base/brass cartridge ammunition in its 6.8x51mm (.277 Sig FURY) used with the XM5 and XM250. The steel base accepts chamber pressures to 80,000psi. The round is also 20 percent lighter than full brass. It is, however, likely more costly which is one reason, as US Army GBen William Boruff Joint PEO, Armaments and Ammunition explained the Army is also buying a full brass 6.8mm with less performance for range/training”. The other approach comes from True Velocity (TVI) which employs a specialised polymer composite case with stainless steel case head. TVCM rounds are 30 percent lighter than brass/metal cased meaning with 5.56 a basic load of 2100 rounds comes in at 3.9 lbs (1.8kg) against 5.6lbs (2.5kg) with brass. A soldier could carry 300 rounds for the same weight – a major advantage in a firefight. In addition, TVCM provide consistent velocity between shots, as confirmed by an evaluation by Richard Mann as detailed in his report in the National Rifle Association Shooting Illustrated web site. It stated TVCM “produced velocities closer to advertised than any other load tested… only 8 ft/s deviation”. The round case also does not conduct heat from the firing to the chamber reducing barrel overheating a major concern with sustained fires. In fact, fired cases are cool to the touch. According to Patrick Hogan, chief of sales and marketing “TVI has already demonstrated its TVCM 6.8x51mm in an upgrade to 7.62x51mm NATO chambered guns by simply changing the barrels. These then gain the ballistic, lethality, and weight benefits with minimal investment”.

True Velocity’s Composite (CM) cased ammunition
True Velocity’s Composite (CM) cased ammunition offer performance and logistics benefits over conventional brass-case ammunition. It is 30 percent lighter, accepts higher chamber pressures, offers consistent velocities between shot, and reduces weapon overheating. (TVI)

Back to Basics

Despite being the most widely fielded weapon in every military, the individual shoulder fired weapons are not simple. Their features, capabilities and performance are a complex balance against very often contradictory requirements. In fact, the appreciation of the various factors involved in the weapon itself and its ammunition are only two of the dynamics that influence the suitability and effectiveness of these weapons for combat. Today one must also consider the sighting/fire controls, the suitability for mounting various shooting aids and accessories, and increasingly new functions like noise suppressors. In the end, however, it is the perspectives of many aspects of combat that each military user/agency has of the battlefield and threats it will face that will drive their stated requirements and, therefore, the weapons that they will seek and put into the hands of each soldier.

by Stephen W. Miller