Lewis Gun profile: build, figures, cartridge and adoption

The Lewis Gun was a gas operated long stroke, open bolt light machine gun introduced in 1914¹ and discontinued in 1953. In the catalogue record it appears here in its Birmingham Small Arms Company form, linking the design to Birmingham Small Arms Company as the principal British manufacturer associated with its wartime and post-war service.

Its baseline figures define the type clearly. Empty weight was 13,000 g, overall length 1,280 mm and barrel length 670 mm. Feed came from a 47-round drum magazine. The recorded cyclic rate was 550 rpm. With its listed chambering, the gun is recorded at 744 m/s muzzle velocity and 3,132 J muzzle energy, with an effective range of 800 m and a maximum range of 3,200 m.

Those figures matter because they place the Lewis in the category of light machine guns that were portable in organisation and role, but still substantial in mass and barrel length. This article covers how that layout was built, what the dimensions and ballistic figures indicate, how the .303 British cartridge fits the recorded performance, and which forces adopted the weapon across its service life.

How the gun is built

The recorded construction of the Lewis Gun is straightforward. Its receiver is steel, its barrel is steel, and its stock is wood. The listed finish is blued. In material terms, that means the main stressed parts are metal, while the rear furniture is separate and organic, a common division of labour in firearms of this period.

The barrel specification adds two useful details. Rifling twist is one turn in 254 mm¹, and the bore has 5 grooves. Those figures describe the internal form that imparts spin to the bullet, and they are part of the gun’s recorded mechanical identity alongside its gas operated long stroke action and open bolt firing system.

Externally, the Lewis is defined by the arrangement described in the catalogue: an aluminium finned barrel radiator enclosed within a cylindrical cooling shroud. That feature matters because it distinguishes the gun at a glance from other contemporary machine guns and because it is tied directly to the weapon’s recorded air cooled design. The barrel remains a steel component, but the surrounding radiator and shroud form the characteristic housing around it. In practical descriptive terms, the Lewis is therefore built as a steel barreled and steel receivered light machine gun with a wooden stock, whose most recognisable element is not the receiver or stock but the shrouded cooling assembly around the barrel.

What the figures show

The recorded figures place the Lewis Gun at the larger end of what was classed as a light machine gun in its period. Empty weight is 13 kg¹, overall length is 1,280 mm and barrel length is 670 mm. Those dimensions matter because they show a gun built around automatic fire from a dedicated support arm, not around the proportions of an ordinary service rifle.

Its feed system points the same way. The standard magazine is a 47-round drum mounted on top of the receiver, and the cyclic rate is 550 rounds per minute. In combination, those figures describe a weapon arranged to deliver repeated bursts with a larger ready supply than a rifle magazine, while retaining a self-contained magazine system rather than belt feed.

The barrel dimensions also fit that role. A 670 mm barrel, with 5 grooves and a 254 mm twist, is substantial in relation to the gun’s 1,280 mm overall length. That helps explain why the listed ballistic figures sit so close to the main cartridge associated with the type, the .303 British. The Lewis is recorded at 744 m/s and 3,132 J. The cartridge’s typical figures are 744 m/s and 3,120 J. Velocity is identical, and muzzle energy differs by 12 J². That close match indicates that the catalogue entry reflects standard .303 British performance rather than an unusual loading.

The .303 British cartridge in the Lewis

The main Lewis chambering was .303 British, a rimmed bottleneck cartridge introduced in 1889³. In catalogue terms, that means a case with a projecting rim and a tapered body with a defined shoulder. Its recorded dimensions are 56.44 mm case length, 78.11 mm overall length and 7.92 mm bullet diameter. The neck diameter is 8.64 mm, the shoulder diameter 10.19 mm, the base diameter 11.68 mm and the rim diameter 13.72 mm.

Pressure data also helps place it. The listed maximum pressure is 365 MPa, also published as 52,939 psi. The case material is brass and the primer is large rifle. The typical bullet weight is 11.28 g.

The Lewis Gun was chambered for both .303 British and .30-06 Springfield, but the .303 loading is the clearest fit for the figures used here. The gun’s listed muzzle velocity is 744 m/s¹, which matches the cartridge’s typical muzzle velocity of 744 m/s exactly. Its listed muzzle energy is 3,132 J, against the cartridge’s typical 3,120 J, a difference of 12 J². That close agreement matters because it ties the firearm record to a specific, documented cartridge profile rather than to a general class of rifle ammunition.

Who adopted it, and when

The adoption record shows broad and early international uptake. The first catalogued adopter was the Belgian Army in 1913¹, as Mitrailleuse Lewis. In 1915 the list expands quickly: the Australian Imperial Force, British Army, Canadian Expeditionary Force, French Army, New Zealand Military Forces, Royal Flying Corps / Royal Air Force and Royal Navy all appear in that year. That timing matches the contemporary summary, "In July 1915, the Lewis gun was supplied to the troops on the Western Front" (source).

Later adoptions extend across Europe, North America, Asia and the Middle East. The Imperial Russian Army and both United States services listed here adopted it in 1917. Further users followed from 1918 to 1922, including Finland, Estonia, Poland, the Royal Netherlands Army and the Irish Defence Forces. The record then continues with the Imperial Japanese Navy in 1932, the British Home Guard in 1940 and the Israel Defense Forces in 1948.

The chart below shows where the concentration lies. Of the 29 catalogued users, 16 fall in the 1910s, 3 in the 1920s, 1 in the 1930s and 2 in the 1940s. That pattern matters because it places the Lewis Gun’s main adoption wave in the First World War period, while also showing a service life that continued well beyond it.

For the full adoption list and base specification, see the Lewis Gun catalogue page.

Source: GET /v1/firearms/lewis-gun/users

The data in this chart

Decade	Armed forces and agencies adopting
1910s	16
1920s	3
1930s	1
1940s	2

Materials and densities

Sources and methods

Footnotes

1. GunSpec catalogue record for the Lewis Gun, which cites militaryfactory.com, modernfirearms.net, britannica.com, firstworldwar.com. In the API: firearms reference. ↩ ↩² ↩³ ↩⁴ ↩⁵

2. Method, comparisons: a difference is one catalogue figure minus another of the same kind, in the same unit. Comparisons. ↩ ↩²

3. GunSpec catalogue record for the .303 British, which cites en.wikipedia.org. In the API: calibers reference and ammunition reference. ↩