Know this is a trivial question to a lot of you, but was wondering what the second number mean in cartridge definitions such as: 6.5 x 50 or 6.5 x 54, 7.7 x 58. Is the 50,54,58 a length desination of the case?

It's the length of the cartridge case in mm.

Case length it is, provided it is preceded by a X. In 45-70, 70 does not designate the case length.

quote:

Case length it is, provided it is preceded by a X. In 45-70, 70 does not designate the case length.

True!
There`s also cases where the last digits are the parent case, 22-250, or 7-08. Then things change again with rounds like the "475 #2 nitro" or .450/ 3 1/4", and once more when the first number is the parent case and the last the caliber in something like the .450/.400. How about the .450/.400 (3")? or 450/400 (3 1/4")? The guy designing one just tosses his name on the end and we have a cartridge like the .257 Robt.
Cartridges have been named in every way one can think of. There is no set pattern,I get a headache just trying to keep them sorted.

And then we look at the first number and try to make sense of it, too.

Like, what's the difference in bore diameter between the 7.5 x 55 Swiss and the 7.62 x 51 NATO? Answer, nothing! They both take .308 bullets.

7.5mm and 7.62mm are different by about .005" Yes, both cartridges use a basic .308 groove dia. The Swiss and most,if not all the European militaries use a land height typically of .006-7" compared to US typical land heights of .004". The 7.62 bore is .300" and the 7.5 bore is .295-6" I think these numbers make sense. Best-o-Luck

And then there is the 30-03 that was replaced by the 30-06 in 1906.

And what about the 38 special and the 357 Magnum, both having the same bore diameter.

The Europeans are not quite as bad, but why does the 8X57 use a bullet that is 8.2mm in diameter while the 9.3X62 uses a 9.3mm diameter bullet.

And the .270 is almost a true 7mm while the 7mm's are near 7.16 mm if I remember correctly.

Thanks now I'm

I thought by now someone would have mentioned the 250/3000. Or adding the bullet weight.
Some cartridges go by the bore size (before rifleing), some times the bullet is changed but not the name. This happened when they went fron heeled bullets to inside lubed bullets. The chamber stayed the same,and the bullets got smaller.
If you want to find a pattern you will go nuts.
Good Luck!

I once did an excel spreadsheet with a bunch of bullet numbers. If it shows up below it means my cut and paste worked.

Bullet European True bullet
Diameter Name diameter in mm
(in inches) (rounded)

0,243 6mm 6,17mm
0,264 6,5mm 6,71mm
0,277 Cal. .270 7,04mm
0,284 7mm 7,21mm
0,308 Cal. .30 (7,62mm) 7,82mm
0,323 8mm 8,20mm
0,338 Cal. .338 8,59mm
0,358 Cal. .35 9,09mm
0,366 9,3mm 9,30mm
0,375 Cal. .375 9,53mm
0,416 Cal. .416 10,57mm

My bullet table didn't show up as planned. The first number on any line is the bullet diameter in inches. The second number is the commonly applied term in Europe for that diameter. The third number is the actual bullet diameter in mm.

There's a book out called, "Cartridges of the World," that lists most of the worlds calibers. It will drive you bonkers figuring out how some of these cartridges acquired their designations. Actually it's a good read. I'd reccomend it.
Best wishes.

Cal - Montreal

quote:

Originally posted by Cal Sibley:
There's a book out called, "Cartridges of the World," that lists most of the worlds calibers. It will drive you bonkers figuring out how some of these cartridges acquired their designations. Actually it's a good read. I'd reccomend it. Best wishes. Cal - Montreal

Actually, COTW is an extremely good publication to have next to your computer as a referene at all times. About the only problem is that different editions contain different cartridges in some categories - like wildcats and proprietary cartridges, which keep increasing in number. Another good reference to have is one of the cartridge conversion pubs, (like George Nonte's book) which tell you what kind of brass to use to make other cases, and the bullet sizes/critical dimensions of the round you are interested in making.