Gas-checks [1] were attachments to ammunition that revolutionised the performance of RML heavy guns. [2] The first generation of RML heavy guns began entering service in about 1865. They all had Woolwich rifling [3] and relied on studs on the projectiles for rotation. Gas-checks were first introduced in 1878 or soon after. They significantly reduced wear on the guns while also increasing their range and accuracy. Before long, studless ammunition was being manufactured for these guns, using gas-checks for projectile rotation. Gas-checks also facilitated a switch to the second generation of RML guns which used polygroove rifling and only supported studless ammunition.
The first RML heavy guns were introduced into British service in about 1865. By 1878, 11 models of Woolwich rifled guns had been introduced, ranging from 7 inches to 12.5 inches. [4] Unfortunately, Woolwich rifling had a major defect, namely, that hot powder gas escaping around the ammunition ("Windage") caused excessive barrel erosion, especially in the rifling grooves. [5] Extensive research was performed in the early 1870s to find a solution, and by 1878 two types of gas-checks had been designed. Both gas-checks were made of copper with a little added zinc. They were, in effect, shallow cups of about the same diameter as the ammunition that were attached to the base of the ammunition. When the gun was fired, the powder gas pressure forced the sides of the cup into the rifling grooves, creating a gas seal. It was immediately found that gas-checks also increased the range of guns, and provided greater accuracy. It was also realised that gas-checks were capable of rotating the ammunition, removing the need for studs. This facilitated the use of polygroove rifling, which used a lot of shallow grooves, in place of the Woolwich system which used only a few deeper grooves. Polygroove rifling was less detrimental to the strength of the guns. Also, studless ammunition was stronger and flew more accurately than studded ammunition. Shell strength was particularly important for armour-piercing ammunition.
Attached gas-checks were used with the existing studded ammunition of Woolwich rifled guns. Their basic design was the same across all sizes of guns, the key difference being their diameter. The gas-check was attached to the base of the projectile by a screw-in plug which required a minor modification to each projectile. A few projectiles were unsuitable for modification, and were scrapped.
Fig 1 shows the base of a 9-inch studded Palliser shell with attached gas-check Mk I. The gas-check consists of a wavy disc with a circular collar of the same diameter as the projectile around its edge. On firing, the intense powder gas pressure flattened the disc against the base of the projectile, increasing the disc’s overall diameter, and forcing the collar against and into the rifling, forming a gas seal. The Mk I gas-check performed well for the faster burning R.L.G. powder with which it was initially tested, but was found to seal the grooves too slowly with slower burning powders such as P and P2, resulting in scoring of the bottoms of grooves. As a result, the Mk I gas-check was superseded by the Mk II gas-check by 1881. Fig 2 shows a 9-inch studded common shell with a Mk II gas-check. The Mk II gas-check was virtually identical to the Mk I, the main difference being that the collar had projections that fitted into the grooves on loading and resulted in faster gas sealing on firing. [8]
Automatic gas-checks [9] were used with studless ammunition in both Woolwich and polygroove rifled guns. They were otherwise known as “Rotating Gas-Checks” [10] or “EOC Gas-Checks”. [11] They were called "automatic" because they could be loaded into the barrel separately from the projectile, and automatically became firmly attached to the projectile on firing. They were called rotating gas-checks because they were able to rotate the projectile, enabling the use of studless projectiles. They were called EOC gas-checks, because they were developed by the Armstrong company which owned EOC. [12]
Automatic gas-checks were designed to be inserted into the barrel separately from, and before, the projectile, so that the gas-check would become located on the base of the projectile, but not attached to it, during ramming. On firing it became firmly attached to the projectile, and remained firmly attached all the way to the target. As an alternative to loading the gas-check separately, it was also sometimes permissible to pre-attach the gas-check to the projectile before loading. [13]
Fig 3 shows the base of a 10-inch studless common shell Mk I with automatic gas-check in place but not attached i.e. as it would be in the gun after ramming but before firing. The centre of the base of the projectile has a circular flat-topped protrusion with undercut sides. The outside of the base is curved and covered with two circular grooves and 47 tapered radial ridges. The collar has 7 projections corresponding to the rifling grooves. On firing, the powder gas pressure forces the copper gas-check into the undercut in the side of the protrusion, the two circular grooves, and the 47 gaps between the tapered radial ridges, permanently attaching the gas-check to the shell. The gas pressure also forces the collar outwards against the rifling, creating a gas seal. The radial ridges prevent rotation of the gas-check on the base of the projectile, forcing the projectile to rotate. [16]
Fig 4 shows a 10-inch studless Palliser shell Mk II with automatic gas-check. The gas-check is the same as the one in Fig 3. However, in contrast to Fig 3, the protrusion on the base of the shell in Fig 4 is not part of the shell, but is instead a wrought iron disc attached to the shell by the screw plug. Initially, all studless shells 9–17.72 inches, including Palliser shells, were made in one piece as in Fig 3. These shells were identified as Mark I. However, it was found that casting Palliser shells in brittle metal in one piece was extremely difficult, especially for smaller calibres, and that the protrusions were liable to chipping during handling. As a result, later Palliser shells 9–12.5 inches were made in two pieces as in Fig 4, and identified as Mark II. The separate protrusions were made from wrought iron, cast steel or malleable cast iron. [17]
Some Woolwich groove guns had 2 marks of automatic gas-checks. The changes to Mark I mainly involved shaving metal off parts of the projections to make them bend more precisely and rapidly into the Woolwich grooves, sealing the grooves faster. [16]
In general, all marks of a particular gun shared the same studless ammunition. Also, the studless ammunition for a particular gun used the same automatic gas-check, except for 9 inch and 10 inch guns which had some marks with Woolwich rifling, and others with polygroove. In these cases there was one automatic gas-check for all Woolwich marks, and a different automatic gas-check for all polygroove marks. The 8 inch 46 cwt and 70 cwt howitzers shared the same studless ammunition, but required different automatic gas-checks for their Woolwich and polygroove rifling respectively. [18]
Images 2–8 show the range of ammunition for the RML 12.5 inch gun in 1885. [20] This range is typical of the ammunition in use with Woolwich-grooved guns of 9 inches or larger after the mid-1880s. These guns no longer fired studded ammunition without gas-checks. Instead there were two sets of ammunition available, namely: older studded ammunition with attached gas-checks Mk II, and newer studless ammunition with automatic gas-checks. Case ammunition was neither studded nor required gas-checks.
The table summarises the types of projectiles in service with RML heavy guns in 1902, (and probably, by the late 1880s for the guns existing at that time). All polygroove guns exclusively fired studless projectiles with automatic gas-checks. All Woolwich groove guns except 7 inch guns, fired both studded and studless projectiles. The studded projectiles had attached gas-checks while the studless projectiles had automatic gas-checks. The 8 inch gun only fired one studless projectile, a studless pointed common shell. The 7 inch guns fired exclusively studded projectiles without gas-checks.
Model [21] | Rifling | Stud/Gas-Check Combinations | |||
---|---|---|---|---|---|
Type | Grooves | Studded without Gas-Check | Studded with Attached Gas-Check | Studless with Automatic Gas-Check | |
17.72 inch [22] | Polygroove | 28 | Y | ||
16 inch [23] | Polygroove | 33 | Y | ||
12.5 inch [24] | Woolwich | 9 | Y | Y | |
12 inch 35 ton [25] | Woolwich | 9 | Y | Y | |
12 inch 25 ton [26] | Woolwich | 9 | Y | Y | |
11 inch [27] | Woolwich | 9 | Y | Y | |
10.4 inch 28 ton [28] | Polygroove | 21 | Y | ||
10 inch 18 ton Marks I & II [29] | Woolwich | 7 | Y | Y | |
10 inch 12 ton Marks III & IV [29] | Polygroove | 32 | Y | ||
9 inch Marks I-V [30] | Woolwich | 6 | Y | Y | |
9 inch Mark VI LS [30] | Polygroove | 27 | Y | ||
8 inch 9 ton gun [31] | Woolwich | 4 | Y | Y [32] | |
8 inch 70 cwt howitzer [33] | Polygroove | 24 | Y | ||
8 inch 46 cwt howitzer [34] | Woolwich | 4 | Y | Y | |
7 inch 7 ton | Woolwich | 3 | Y | ||
7 inch 6.5 ton | Woolwich | 3 | Y | ||
7 inch 90 cwt | Woolwich | 3 | Y | ||
Rotation of ammunition is a term used with reference to guns. Projectiles intended for RML guns were at first fitted with a number of gun-metal studs arranged around them in a spiral manner corresponding to the twist of rifling. Invented in mid-1840s by Giovanni Cavalli, this method was defective, as it allowed, as in the old smooth-bore guns, the powder gas to escape by the clearance between the projectile and the bore, with a consequent loss of efficiency; it also quickly eroded the bore of the larger guns. Multiple solution to the problems were invented in two following decades, both for muzzle-loaders and breech-loaders.
Palliser shot is an early British armour-piercing artillery projectile, intended to pierce the armour protection of warships being developed in the second half of the 19th century. It was invented by Sir William Palliser, after whom it is named.
This article explains terms used for the British Armed Forces' ordnance (weapons) and ammunition. The terms may have different meanings depending on its usage in another country's military.
A muzzle-loading rifle is a muzzle-loaded small arm that has a rifled barrel rather than a smoothbore, and is loaded from the muzzle of the barrel rather than the breech. Historically they were developed when rifled barrels were introduced by the 1740ies, which offered higher accuracy than the earlier smoothbores. The American longrifle evolved from the German "Jäger" rifle; a popularly recognizable form of the "muzzleloader" was the Kentucky Rifle. Although by definition they must be reloaded after each shot in a time-consuming fashion, they are still produced for hunting.
An Armstrong gun was a uniquely designed type of rifled breech-loading field and heavy gun designed by Sir William Armstrong and manufactured in England beginning in 1855 by the Elswick Ordnance Company and the Royal Arsenal at Woolwich. Such guns involved a built-up gun construction system of a wrought-iron tube surrounded by a number of wrought-iron strengthening coils shrunk over the inner tube to keep it under compression.
The 100-ton gun was the heaviest gun of the world for quite some time and got a lot of media attention. It was a 17.72-inch (450 mm) rifled muzzle-loading (RML) gun made by Elswick Ordnance Company, the armaments division of the British manufacturing company Armstrong Whitworth, owned by William Armstrong. The 15 guns Armstrong made were used to arm two Italian battleships and, to counter these, British fortifications at Malta and Gibraltar.
The RML 6.3-inch howitzer was a British rifled muzzle-loading "siege" or "position" howitzer/mortar proposed in 1874 and finally introduced in 1878 as a lighter version of the successful 8-inch howitzer that could be carried by the existing 40-pounder gun carriage.
The RML 10-inch guns Mk I – Mk II were large rifled muzzle-loading guns designed for British battleships and monitors in the 1860s to 1880s. They were also fitted to the Bouncer and Ant-class flat-iron gunboats. They were also used for fixed coastal defences around the United Kingdom and around the British Empire until the early years of the 20th century.
The RML 9-inch guns Mark I – Mark VI were large rifled muzzle-loading guns of the 1860s used as primary armament on smaller British ironclad battleships and secondary armament on larger battleships, and also ashore for coast defence. It should not be confused with the RML 9-inch Armstrong Gun, used by the Dutch navy, the Spanish Navy, and other navies.
The RML 12.5-inch guns were large rifled muzzle-loading guns designed for British battleships and were also employed for coast defence.
RML 16-inch 80-ton guns were large rifled muzzle-loading guns intended to give the largest British battleships parity with the large guns being mounted by Italian and French ships in the Mediterranean Sea in the 1870s.
The RML 12-inch 25-ton guns were large rifled muzzle-loading guns of mid-late 1800s used as primary armament on British ironclad turret battleships and coastal monitors, and also ashore for coast defence. They were the shorter and less powerful of the two 12-inch (305-mm) British RML guns, the other being the 35-ton gun.
RML 12-inch 35-ton guns were large rifled muzzle-loading guns used as primary armament on British battleships of the 1870s. They were the longer and more powerful of the two 12-inch British RML guns, the other being the 25-ton gun.
RML 11-inch 25-ton guns were large rifled muzzle-loading guns used as primary armament on British battleships and for coastal defence. They were effectively the same gun as the RML 12-inch 25-ton gun, bored to 11 inches instead of 12.
The RML 7-inch guns were various designs of medium-sized rifled muzzle-loading guns used to arm small to medium-sized British warships in the late 19th century, and some were used ashore for coast defence.
The British RML 8-inch 9-ton guns Mark I – Mark III were medium rifled muzzle-loading guns used to arm smaller ironclad warships and coast defence batteries in the later 19th century.
An attached gas-check was a copper plate that was physically attached to the base of a studded projectile of rifled muzzle-loading ("RML") artillery, sealing the escape of gas between the projectile and the barrel.
A rotating gas-check was a copper plate that automatically attached itself to a specially-designed studless projectile of rifled muzzle-loading ("RML") artillery, sealing the escape of gas between the projectile and the barrel and imparting axial rotation to the projectile.
The RML 8-inch howitzer was a British Rifled, Muzzle Loading (RML) Howitzer manufactured in England in the 19th century, which fired a projectile weighing approximately 180 pounds (82 kg). It was used in siege batteries and in fortifications.
The RML 6.6 inch howitzer was a British Rifled, Muzzle Loading (RML) Howitzer manufactured in England in the 19th century, which fired a projectile weighing approximately 100 pounds (45 kg). It was used in siege batteries and in fortifications.