Gas-checks[1] were attachments to ammunition that revolutionised the performance of RML heavy guns.
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.
[5] Extensive research was performed in the early 1870s to find a solution, and by 1878 two types of gas-checks had been designed.
It was immediately found that gas-checks also increased the range of guns, and provided greater accuracy.
Attached gas-checks were used with the existing studded ammunition of Woolwich rifled guns.
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.
[8] Automatic gas-checks[9] were used with studless ammunition in both Woolwich and polygroove rifled guns.
[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.
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.
[16] Fig 4 shows a 10-inch studless Palliser shell Mk II with automatic gas-check.
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.