450/400, 500/450 etc

[kurly]

I have always been intrigued by the calibre designations 450/400, 500/450 etc etc. I know the first figure indicates the bullet size but what does the second figure indicate/ signify

[Ross]

Depends if it is USA designation or European.

USA = 45-70 Govt. = 45 calibre / 70 grains black powder
Euro = 500/450 = 500 case / 450 calibre bullet, i.e. 500 case necked down to 450 calibre

e.g. Martinin Henry 577 / 450 = 577 case necked down to 450 calibre

[Sean Murphy]

The ones you mention are old British caliber designations.

The first number in for example 500/450 denotes the diameter of the parent case body. In this case 500. The 450 denotes the nominal caliber of the projectile. So the old 500/450 featured a .500 diameter case necked down to nominal .450.

Another example is the .577/450 Martini Henry. A .577 case necked down to .450.

This is how the British designated bottle necked cases. A particular cartridge may also have a further name designation. eg. 577/450 Martini Henry or 500/450 Westley Richards No 2 Musket. Cartridges were often named by the gunmaking firms who developed them or the rifles they were adopted in. This method originated with the birth of self contained Black powder cartridges.

The Americans had a different way of doing things. Example 45-70. In this method the first number denotes the nominal caliber and the second is the size of the Black powder load in grains. So a 45-70 is a .45 caliber bullet propelled by 70gr of BP. Originally the weight of the bullet also featured in the name. This was done mostly by the military to denote different loads for different arms. The 45-70 was originally the 45-70-500 denoting a 500gr bullet being used. This cartridge gave unacceptable recoil when used in the lighter Springfield Cavalry Carbine so a ligher bullet was adopted for the cavalry and so the 45-70-405 cartridge came into service.

This method was obviousely started during the BP cartridge era but was carried over into the smokeless era for a short time. That is where we get cartridges like the 30-30 Winchester, 30-40 Krag Jorgenson, 25-20, 32-40 etc etc etc. The powder number now designating the load of smokeless powder. This was ok in the beginning when smokeless was smokeless but later as more sophisticated smokeless powders were developed with varying burning rates it became impractical and the yanks started to name their cartridges by caliber and inventor.

Sean.

[Sean Murphy]

The Europeans have always used the metric system. One of the first cartridges from Europe was the 11mm Mauser. This was named for it's caliber and inventor. Later as more and more cartridges came onto the scene the Europeans started using case dimentions as well to avoid confusion, eg 7X57 Mauser. This is a 7mm nominal diameter bullet in a bottleneck case that is 57mm long originally chambered in a rifle offered by Mauser.

However, there is much room for confusion in the world of cartridges. For example: Do you know that the .308 Winchester fires a smaller diameter bullet than the .303 British. The 308 fires a bullet of .308 inch diameter while the 303 fires a bullet of .311 inch diamter. WTF. Why the misnomer then. Simple, the americans named their modern cartridges for the actuall bullet diameter which conforms usually to the largest diameter inside the bore, ie. the Groove diameter. The British however named many of their cartidges for the Bore diameter which is the smaller dimention within the bore, otherwise known as the Land diameter. So the .308 is in fact a 30 caliber weapon with a groove diameter of .308 (4 thou groove depth). The .303 is a .303 bored weapon with a groove diameter of .311 (also 4 thou grooves ). Many other older british calibers have similar "incorrect" designations.

Sean.