Editing Caliber (section)

==Pounds as a measure of cannon bore==
Smoothbore [[cannon]] and [[carronade]] bores are designated by the weight in imperial pounds of spherical solid iron shot of diameter to fit the bore. Standard sizes are 6, 12, 18, 24, 32, and 42 pounds,<ref>British cannonball sizes. Available at: https://2015fallhw.github.io/arcidau/Cannonballs.html (Accessed: 09 September 2023).</ref> with some non-standard weights using the same scheme. See [[Carronade#Ordnance]].

From about the mid-17th until the mid-19th century, the measurement of the bore of large gunpowder weapons was usually expressed as the weight of its iron shot in [[Pound (mass)|pounds]].  Iron [[round shot|shot]] was used as the standard reference because iron was the most common material used for artillery ammunition during that period, and solid spherical shot the most common form encountered. Artillery was classified thereby into standard categories, with the 3-pounder, 4-pounder, 6-pounder, 8-pounder, 9-pounder, 12-pounder, 18-pounder, 24-pounder, and 32-pounder being the most common sizes encountered, although larger, smaller and intermediate sizes existed.

In practice, though, significant variation occurred in the actual mass of the projectile for a given nominal shot weight. The country of manufacture is a significant consideration when determining bore diameters. For example, the French [[Pound (mass)#French livre|livre]], until 1812, had a mass of {{convert|489.5|g|lb|abbr=on}}, whilst the contemporary English ([[avoirdupois]]) pound massed of approximately {{convert|454|g|lb|abbr=on}}. Thus, a French 32-pounder at the  [[Battle of Trafalgar]] threw a shot with {{convert|1.138|kg|lb|abbr=on}} more mass than an English 32-pounder.

Complicating matters further, muzzle-loaded weapons require a significant gap between the sides of the tube bore and the surface of the shot. This is necessary so the projectile may be inserted from the mouth to the base of the tube and seated securely adjacent the propellant charge with relative ease. The gap, called [[windage]], increases the size of the bore with respect to the diameter of the shot somewhere between 10% and 20% depending upon the year the tube was cast and the [[foundry]] responsible.

{| class="wikitable"
|-
|+English gun classes c. 1800{{Citation needed|date=April 2010}}
|-
! gun class (pdr.)
!projectile mass (kg)
! shot diameter (cm)
! shot volume (cm<sup>3</sup>)
! approx. service bore (cm)
|-
| align="center"| 2
| align="right"| {{convert|0.9|kg|lb|abbr=on}}
| align="right"| {{convert|6|cm|in|abbr=on}}
| align="right"| {{convert|115|cm3|cuin|abbr=on}}
| align="right"| {{convert|6.6|cm|in|abbr=on}}
|-
| align="center"| 3
| align="right"| {{convert|1.4|kg|lb|abbr=on}}
| align="right"| {{convert|6.9|cm|in|abbr=on}}
| align="right"| {{convert|172|cm3|cuin|abbr=on}}
| align="right"| {{convert|7.6|cm|in|abbr=on}}

|-
| align="center"| 4
| align="right"| {{convert|1.8|kg|lb|abbr=on}}
| align="right"| {{convert|7.6|cm|in|abbr=on}}
| align="right"| {{convert|230|cm3|cuin|abbr=on}}
| align="right"| {{convert|8.4|cm|in|abbr=on}}

|-
| align="center"| 6
| align="right"| {{convert|2.7|kg|lb|abbr=on}}
| align="right"| {{convert|8.7|cm|in|abbr=on}}
| align="right"| {{convert|345|cm3|cuin|abbr=on}}
| align="right"| {{convert|9.6|cm|in|abbr=on}}

|-
| align="center"| 9
| align="right"| {{convert|4.1|kg|lb|abbr=on}}
| align="right"| {{convert|10|cm|in|abbr=on}}
| align="right"| {{convert|518|cm3|cuin|abbr=on}}
| align="right"| {{convert|11|cm|in|abbr=on}}

|-
| align="center"| 12
| align="right"| {{convert|5.4|kg|lb|abbr=on}}
| align="right"| {{convert|10.9|cm|in|abbr=on}}
| align="right"| {{convert|691|cm3|cuin|abbr=on}}
| align="right"| {{convert|12.1|cm|in|abbr=on}}

|-
| align="center"| 18
| align="right"| {{convert|8.2|kg|lb|abbr=on}}
| align="right"| {{convert|12.6|cm|in|abbr=on}}
| align="right"| {{convert|1,037|cm3|cuin|abbr=on}}
| align="right"| {{convert|13.8|cm|in|abbr=on}}

|-
| align="center"| 24
| align="right"| {{convert|10.9|kg|lb|abbr=on}}
| align="right"| {{convert|13.8|cm|in|abbr=on}}
| align="right"| {{convert|1,383|cm3|cuin|abbr=on}}
| align="right"| {{convert|15.2|cm|in|abbr=on}}

|-
| align="center"| 32
| align="right"| {{convert|14.5|kg|lb|abbr=on}}
| align="right"| {{convert|15.2|cm|in|abbr=on}}
| align="right"| {{convert|1,844|cm3|cuin|abbr=on}}
| align="right"| {{convert|16.7|cm|in|abbr=on}}

|-
| align="center"| 64
| align="right"| {{convert|29|kg|lb|abbr=on}}
| align="right"| {{convert|19.2|cm|in|abbr=on}}
| align="right"| {{convert|3,687|cm3|cuin|abbr=on}}
| align="right"| {{convert|21.1|cm|in|abbr=on}}

|}

The relationship between bore diameter and projectile weight was severed following the widespread adoption of rifled weapons during the latter part of the 19th century. Guns continued to be classed by projectile weight into the mid-20th century, [[British standard ordnance weights and measurements|particularly in British service]] with guns, such as the [[Ordnance QF 2-pounder|2-pounder]], [[Ordnance QF 6-pounder|6-pounder]],  and [[Ordnance QF 17-pounder|17-pounder]] [[Anti-tank warfare|anti-tank weapons]]. However, this value no longer definitively related to bore diameter, since projectiles were no longer simple spheres—and in any case were more often hollow shells filled with explosives rather than solid iron shot.