RML 7-inch gun

These guns were the first to incorporate the new "Woolwich" rifling system, a modification of the French system, of from 3 – 9 broad shallow grooves after Britain abandoned the Armstrong "shunt" rifling system in May 1865 : "...M.L. 7 in (18 cm) guns in course of manufacture were rifled on this principle, upon which all of our heavy pieces since have been rifled. The 7 in (18 cm) referred to, and introduced into the service in 1865, were the first of the so-called Woolwich guns, which then meant "wrought iron M.L. guns built up on Sir W. Armstrong's principle, improved upon by hooking the coils over one another, and having solid ended steel barrels, rifled on the system shown above, for studded projectiles".^[4]

All versions were constructed of a steel A tube surrounded by various numbers and thicknesses of wrought-iron coils. Rifling was 3 grooves with a uniform 1 turn in 35 calibres i.e. in 245 in (620 cm).^[2]

The diagrams below show the progression from the original expensive Armstrong construction in Mk I of multiple relatively thin coils, through to the simplified and cheaper Woolwich design of Mk III.

• 
  The 4 Marks of 7 ton gun
• 
  The 3 Marks of 6½ ton gun
• 
  90 cwt gun

RML 7-inch 7 ton gun

This was a coast defence gun introduced in 1865 to replace the failed RBL 7-inch Armstrong gun.Three marks were produced.

The primary projectile for 7 ton and 6½ ton guns was Palliser shot or shell for attacking armoured warships, fired with a large "battering" charge for maximum velocity. All guns were also equipped with shrapnel shells for anti-personnel use and explosive common shells for attacking unarmoured targets. The "double" common shell was much longer than the standard common shell, and hence contained approximately twice as much gunpowder. It was unstable in flight and hence inaccurate beyond 2,000 yd (1.8 km) but was considered useful for attacking wooden warships at ranges below 2,000 yd (1.8 km).^[7]

• 
  Mk III Palliser shell
• 
  Mk VI Palliser shot
• 
  Mk III shrapnel shell
• 
  Mk V common shell
• 
  Mk III double common shell

This was the only RML heavy gun not to be issued with gas-checks.

• Restored 6½ ton Mk I Numbers 148 & 163 at Garden Island Rockingham, Western Australia (Fleet Base West). For restoration story see http://www.defence.gov.au/news/navynews/editions/4719/feature/feature06.htm
• Several 6½ ton Mk I guns on Ascension Island
• 6½ ton Mk I at Fort Siloso, Singapore
• 6½ ton Mk III of 1869, at Elizabeth Castle, Jersey, UK
• Remains of several 7 ton Mk III guns on Flat Holm island, UK
• Nine 7 ton Mk III guns on Steep Holm island, UK
• A 7-ton Mk I gun at The Citadel, Nova Scotia, Canada
• A 6½ ton Mk I gun on Signal Hill (Cape Town), South Africa.

• List of naval guns