Gas-checks in British RML heavy guns#Attached Gas-Checks

Gas-checksThe term "gas-check" was hyphenated in late 1880s and early 1900s official British government publications such as treatises on ammunition and handbooks for various guns. were attachments to ammunition that revolutionised the performance of RML heavy guns.In this article, "RML heavy guns" includes rifled muzzle-loading guns and howitzers of 7 inches calibre or larger The first generation of RML heavy guns began entering service in about 1865. They all had Woolwich riflingRef 1877 292; Ref 1879 pp.45 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.

Introduction

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.Ref 1873 pp. 528, 530-533; Ref 1877 p. 292 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.Ref 1878 p. 134 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==

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.

Image:RML 9 inch Palliser Studded Shell Mk IV with Attached Gas-Check Mk I 2of2.jpg | Fig 1.This is part of the image on Ref 1881 p. 182 Attached Gas-Check Mk I.

Image:RML 9 inch Common Studded Shell with Attached Gas-Check Mk II 1of2.jpg | Fig 2.This is part of the image on Ref 1881 p. 187 Attached Gas-Check Mk II.

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.Ref 1887A pp. 152-153

==Automatic gas-checks==

Automatic gas-checksRef 1881 pp. 188-190; Ref 1887A pp. 155-156 were used with studless ammunition in both Woolwich and polygroove rifled guns. They were otherwise known as “Rotating Gas-Checks”Ref 1887A p. 155 or “EOC Gas-Checks”.Ref 1881 p. 188 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.The Armstrong company sold polygroove guns with studless gas-checked ammunition to the Italian navy in about 1874. Ref 1882 pp. 69-72; 100-ton gun

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.Ref 1885 p. 33

Image:RML 10 inch Common Studless Shell Mk I with Automatic Gas-Check 1of2.jpg | Fig 3.This is part of Ref 1887A Plate VIII Protrusion is part of shell.

Image:RML 10 inch Palliser Studless Shell Mk II with Automatic Gas-Check 2of2.jpg | Fig 4.This is part of Ref 1887A Plate VII Protrusion is wrought-iron disk.

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.Ref 1902A p. 235

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.Ref 1902A p. 252

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.

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.Ref 1890 p. 11, Plates V-VII

Gallery

Image:RML 12 inch 35 ton Automatic Gas-Check Mark I Detail.jpg| 1

Image:RML 12.5in Studded Palliser Shell Mk III with Attached Gas-Check Mk II.JPG | 2

Image:RML 12.5in Studded Common Shell with Attached Gas-Check Mk II.JPG | 3

Image:RML 12.5in Studded Shrapnel Shell with Attached Gas-check Mk II.JPG | 4

Image:RML 12.5in Case Shot Mk III.JPG | 5

Image:RML 12.5in Studless Palliser Shell Mk I with Automatic Gas-Check.JPG | 6

Image:RML 12.5in Studless Common Shell Mk I with Automatic Gas-Check.JPG | 7

Image:RML 12.5 inch Studless Shrapnel Shell.jpg| 8

RML 12in Automatic Gas-Check Mk I
RML 12.5in Studded Palliser Shell Mk III with Attached Gas-Check Mk II
RML 12.5in Studded Common Shell Mk I with Attached Gas-Check Mk II
RML 12.5in Studded Shrapnel Shell Mk I with Attached Gas-check Mk II
RML 12.5in Case Shot Mk III
RML 12.5in Studless Palliser Shell Mk I with Automatic Gas-CheckThis Palliser shell Mk I is made in one piece, unkike the 10 inch Palliser shell Mk II in Fig 4 which has a separate base protrusion
RML 12.5in Studless Common Shell Mk I with Automatic Gas-Check
RML 12.5in Studless Shrapnel Shell Mk I with Automatic Gas-check

Images 2–8 show the range of ammunition for the RML 12.5 inch gun in 1885.Ref 1885 pp. 32–33; Plates XI-XIV 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.

Summary table

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.

class="wikitable" style="text-align:center" !rowspan=2; width=170; \| ModelThis article uses the modern terms "Model" and "Mark". During part of the late 1800s, the terms "Nature" and "Pattern" respectively were used instead. Ref 1893 p. 92 !colspan=2 \| Rifling !colspan=3 \| Stud/Gas-Check Combinations
width=130; \|Type \|width=100; \|Grooves \|width=100; \|Studded without Gas-Check \|width=100; \|Studded with Attached Gas-Check \|width=100; \|Studless with Automatic Gas-Check
17.72 inchFour of these guns were purchased for the British service from EOC in 1878 following previous similar sales to Italy. Ref 1893 p.112; Ref 1882 pp. 69-72; 100-ton gun \|style="background:orange" \| Polygroove \|28 \| \| \|Y
16 inchRef 1893 pp. 110-112, 116 \|style="background:orange" \| Polygroove \|33 \| \| \|Y
12.5 inchRef 1885 pp. 32-33, Plates XI-XIV \|style="background:aqua" \| Woolwich \|9 \| \|Y \|Y
12 inch 35 tonRef 1884A pp. 10-12, Plates VI-VIII \|style="background:aqua" \| Woolwich \|9 \| \|Y \|Y
12 inch 25 tonRef 1893 pp. 105-107, 116 \|style="background:aqua" \| Woolwich \|9 \| \|Y \|Y
11 inchRef 1893 pp. 104-105, 116 \|style="background:aqua" \| Woolwich \|9 \| \|Y \|Y
10.4 inch 28 tonRef 1887A pp. 232, 234, 238, 418, 432, 434-436; Ref 1893 pp. 101-104, 116; Ref 1902 p. 337. While the 10.4 inch gun is listed in Ref 1902, it is not listed in 1902A \|style="background:orange" \| Polygroove \|21 \| \| \|Y
10 inch 18 ton Marks I & IIRef 1903 pp. 3-5, 41-46, Plates XXVI-XXXVIII \|style="background:aqua" \| Woolwich \|7 \| \|Y \|Y
10 inch 12 ton Marks III & IV \| style="background:orange" \| Polygroove \|32 \| \| \|Y
9 inch Marks I-VRef 1894 pp. 3-4, 25-29, Plates XIV-XVII \|style="background:aqua" \| Woolwich \|6 \| \|Y \|Y
9 inch Mark VI LS \|style="background:orange" \| Polygroove \|27 \| \| \|Y
8 inch 9 ton gunRef 1893 pp. 96-97, 116 \|style="background:aqua" \| Woolwich \|4 \| \|Y \|YThe 8 inch gun only fired one studless projectile, a pointed common shell. Ref 1902A p. 241
8 inch 70 cwt howitzerRef 1895 pp. 14-17, Plates VI-VII \|style="background:orange" \| Polygroove \|24 \| \| \|Y
8 inch 46 cwt howitzerRef 1900 pp. 15-18, Plates VI-IX \|style="background:aqua" \| 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 \| \|

class="wikitable" style="text-align:center"

!rowspan=2; width=170; | ModelThis article uses the modern terms "Model" and "Mark". During part of the late 1800s, the terms "Nature" and "Pattern" respectively were used instead. Ref 1893 p. 92

!colspan=2 | Rifling

!colspan=3 | Stud/Gas-Check Combinations

width=130; |Type

|width=100; |Grooves

|width=100; |Studded without Gas-Check

|width=100; |Studded with Attached Gas-Check

|width=100; |Studless with Automatic Gas-Check

17.72 inchFour of these guns were purchased for the British service from EOC in 1878 following previous similar sales to Italy. Ref 1893 p.112; Ref 1882 pp. 69-72; 100-ton gun

|style="background:orange" | Polygroove

|28

16 inchRef 1893 pp. 110-112, 116

|style="background:orange" | Polygroove

|33

12.5 inchRef 1885 pp. 32-33, Plates XI-XIV