Carlingnose Battery – Sub-calibre Guns

Gun barrels have a limited life, measured in terms of the number of rounds fired. Each shot removes a little metal from the inside of the barrel, gradually allowing explosive gases to leak past the shell as it was fired and so reducing the muzzle velocity.

For practise firing and gun-laying (verifying the accuracy of the gun sights) a sub-calibre gun could be fitted inside the main gun barrel. The smaller sub-calibre shell did not touch the sides of the main barrel when fired, so there was no wear on the barrel. The 6 inch BL gun handbook 1911 includes a chapter on fitting these smaller calibre guns inside the barrel of the 6 inch guns, for practise gun-laying.

[Thanks are due to Trevor Parker of the Ordnance Society for an explanation of the barrel wear problem, and this extract about Aiming Rifles]

The Fort Record book includes the following range tables for 3-pounder Hotchkiss and Nordenfelt Quick Firing guns.