A shell case is an open topped cylinder with a surface area of 2πrh + πr^2. Using your example of going from 128mm to 130mm, the brass case of a Mark 10 shell for a US 5"/38 gun is 127圆79mm and weighed 5.58kg. That means bigger shells (now you can store less shells), more weight (good luck humping that round, loader), and more material (higher cost per round). When you increase the caliber, and keep the length the same, the volume of the case increases by the square of the caliber. A 3-pound gun is 47mm which explains why we had 47mm weapons. This is how much round, solid shot would weigh and goes waaaaay back in British naval history. Then there's the British "pound" system like the "3-pounder". 12.7cm and 12.8cm are actually 5 inch guns. Sometimes odd metric designations are because they began life in another measurement. So the number in the name is just a name, divorced from the actual engineering specifications. The closest thing to 5.56mm about 5.56mm is the pilot diameter, which is the size of the hole which guides the bullet into the rifling, and even that isn't quite 5.56mm. The bullet is 5.70mm at its thickest, same as its parent the. 9x19mm measures between the grooves, so the bullet is 9mm in diameter.įor example, no part of 5.56x45mm NATO is 5.56mm. 9x18mm Makarov measures caliber between the lands, so the bullet is 9.27mm in diameter. For example 9x19mm Parabellum and 9x18mm Makarov do not have the same bullet diameter. If rifling is involved, you can use the diameter as measured at the lands (the smaller diameter formed by the ridges) or the grooves (the larger diameter formed by the troughs between the ridges). Look at all those numbers to choose from! You can use the chamber diameter, the case diameter, the bore diameter, the bullet diameter. There are so many numbers to choose from! Have a look at 5.56x45mm NATO. Wikipedia puts it this way.ĭue to variations in naming conventions, and the whims of the cartridge manufacturers, bullet diameters can vary widely from the diameter implied by the name. The US 90mm also started as an AA gun (the 90mm M1 and M2) and was adapted into the M3 tank cannon for the M36 Tank Destroyer and M26 Pershing. Naval guns have been around for a long time, so tanks and artillery inherit the naming and size quirks of old naval guns.įor example, the famous German 88 began life as AA gun which itself began as a naval gun. Anti-aircraft guns are often preferred because they're designed to be lighter, and more mobile than naval guns. Both naval and anti-aircraft guns require long range, high muzzle velocity (naval guns for armor penetration, AA for altitude), and large calibers to pack sufficient explosive or kinetic energy to do damage. Large caliber artillery and tank cannons are often adapted from naval guns and anti-aircraft guns (which also often come from naval guns). As a result militaries can afford a lot of diversity in large calibers, but they still tend to cluster around certain historical calibers that they (or who they're buying from) are already producing. These fields were in an intense arms race, particularly during WWII until roughly the 1980s when electronics took over, so you could get an advantage out of fielding a new round that offset the logistical problems. They fill the roles of anti-tank, anti-aircraft, and artillery. Large caliber firearms tend to be specialized, vehicle mounted, and fire less ammunition.
#Higher calibre meaning full
One pistol round (9x19mm or 9×18mm), one intermediate round (5.56x45mm NATO or 5.45×39mm Soviet), and one full power rifle round (7.62×51mm NATO or 7.62×54mmR). For this reason, most militaries, in contrast to civilians, have standardized around just a few small arms rounds. Instead the problem is supplying large amounts to large numbers of troops who will use it for various tasks, and they have to carry it. If all your guns can share ammunition that simplifies production, logistics, and supply.įor small arms, small differences in ballistic performance are not terribly important tactics dominate small arms engagements. Just having the same caliber doesn't mean you can share ammunition, there's many other considerations, but it helps. For example, the German 12.8 cm Pak 44 used tooling in common with the 12.7 cm SK C/34 naval gun used on German destroyers. This is probably the most important reason why large caliber guns are the caliber they are: there's already tooling to produce the parts in that caliber, particularly the expensive rifled barrels. They might start with one neat number, but derived dimensions are subservient to engineering considerations and calculations. The engineers designing and building the gun don't care if it's in neat numbers. The general answer to that is because the design goal is to make the best gun possible, not have the numbers come out neatly. Why not an even value, such as 130 mm? Neat Numbers Don't Kill The Enemy