Reply to post:

Brit gun nut builds working sniper rifle at home out of scrap metal

cnorris517

Ok first off a nomenclature bit.

Calibre refers to the diameter of the projectile (bullet), not length, weight, type or anything else. Sometimes the calibre becomes synonymous with the cartridge but not always. For example .308 is actually .308 winchester and uses a .308 diameter bullet but there are plenty of cartridges that use .308 projectiles eg .30 carbine.

The cartridge is the brass (usually) case in which the propellant is housed and which the projectile is inserted. To add to the confusion the bullet, powder and case once assembled along with the primer are collectively known as a cartridge, bullet or round. Most people use these terms interchangeably.

Anyway back to the point... The story I was told, which makes sense to me at least, is that a lot of the calibres date back to a time when accurate measurement was performed using something little more accurate than a stick. As these calibres evolved from the original low-ish pressure lead ball, which was a bit more tolerant to dimensional differences, to higher pressure jacketed rounds, which really aren't, it became necessary to improve the accuracy of measurement and standardise each calibre.

I have no idea how many "standards" there were/are but the result was/is a selection of common diameter measurements that most cartridges and therefore barrels and projectiles are based off of. If a manufacturer of any of the above wanted to produce a new product (eg a new cartridge) in a new size then it required bullet, barrel and cartridge design whereas using a common calibre allowed them to use off the shelf barrels and bullet heads for their new cartridge.

There were/are exceptions to this. Some more modern projectiles use a new fangled thing called physics to calculate the required parameters for a desired outcome. This results in some fairly weird numbers too. for example the .408 cheytac dates, I think, from the late 90s. Even this though is still caught up a bit in the past as it uses a cartridge case from the older 505 Gibbs.

Then there is the wow factor/bigger is better tendency. This breaks down into three sub-categories

a) Some of the larger cases exist (i believe) purely because a particular number (bigger usually) sounds better. 700 Nitro Express being one of them.

b) Some obscure cartridges were designed purely for a specific purpose, normally military ie body armor defeating (FN 5.7) or a desire to be quieter than usual (300 BLK) but sometimes record breaking (22 Eargesplitten Loudenboomer) - Arguably this falls into the section above I know

So the short answer is

Sometimes it's the legacy of older less accurate measurements being standardised using modern techniques or a change in measuring standard (inch/mm to inner to outer bore)

Sometimes it's the result of research to find the optimal dimensions for a desired end result

Sometimes it's a marketing exercise

POST COMMENT House rules

Not a member of The Register? Create a new account here.

  • Enter your comment

  • Add an icon

Anonymous cowards cannot choose their icon