I need for someone to clarify some of the numbers I see relative to ammunition. Example is 7.62mmx.51mm or .22-50. Are we talking about dimensions in the first and caliber in the second. Or 7MM-08 or 7mm.308. I am sure it is clear to most of you but I could use a lesson or two. Thanks all.

Well there is really no standard rule about naming cartridges, but here is the breakdown on the cartridges ou mentioned.
7.62X51mm the Europeans usually designate cartridges this way, but this on happens to be the military verson of the 308 Win. 7.62mm = .308" which is the bullet diameter, the second number, 51mm is the case length. The 30-06 would be 7.62X63mm.

22-250 is named such because it is a 22 caliber bullet sitting in a necked down 250 Savage case. The 7mm-08 Rem is a 7mm bullet in a necked down 308 Win case.

Some cartridges are named afer a person or the company that developed them, i.e. 454 Casull was invented by Dick Casull, the 270 Win was commercialized by the Winchester company, the 7mm-08 Rem was commercialized by the Remington company.

Some of the older cartridges take their names from the blackpower loads they used to use such as the 45-70 was a 45 caliber bullet over 70 grains of blackpowder, the 44-40 was a 44 caliber over 40 grains, etc.

Then you have wildcats where anything goes. Hope this helps some.

frizellr has provided the meat of the answer to your question. To this I would add a few general comments: The Europeans are a disciplined, intelligent and systematic lot. There is a general standardized pattern to their small-arms cartridge nomenclature. The first number is the bore size in millimeters, the second numer is the case length in millimeters, and, if the round has a rimmed case, they add an "R" at the end of the designation, such as 7.62X54R, (the rimmed full-power Russian military cartridge).

In the U.S. today, and also to some extent in England, there are no rules for cartridge nomenclature AT ALL, although we did have a sort of system in the 19th Century. Everyone who develops a cartridge design names it to suit himself! In the 19th Century, many designers named a cartridge by giving the nominal caliber, the weight of the powder charge, and often, weight of bullet. IE, .45/70/500, a .45 caliber round holding 70 grains of powder and shooting a 500 grain bullet. Still, there could be straight or bottlenecked .45/70/500's, which were obviously different!! However, today, no such system applies in this country! We often (but not invariably) name a cartridge by caliber, either in the metric system or English system, sometimes by bore diameter, sometimes by bullet diameter, then often add the name of the originator, such as 6mm Remington or .244 Remington (both of these apply to the EXACT SAME CARTRIDGE), or give the caliber and date of introduction, such as .30/'06 for a .30 caliber introduced in 1906, etc. But, sometimes we tack on a muzzle velocity, such as .250/3000 Savage! I believe it is safe to say that in the U.S. today, we have no system at all, and you have to become familiar with a whole lot of different cartridges to know which is which!! For example, there are a lot of very different rounds known as .300's, both Magnums and the .300 Savage, which is certainly no magnum!! HELP!!! The British are about as bad off as we!! To really know your cartridges, buy a copy of Barnes" Cartridges of the World (COTW), and really study it! It is interesting a hell, to say the least!!

Keep yore powder dry!!

its a mess, thats about all there is to say. dont try to understand it it will amke you feel dumber. though the good thing is that if you make a cartridge that you can put your name on the end of it

propmahn
save the world, reload your brass

Don't forget the 6.5-08 A-Square which is now the 260 Rem.