Metric to caliber conversion

[Smokey Joe]

And we have a winner!!

Gromky takes the thread, with his comment:

Some good info in this thread....caliber designations have always confused the heck out of me.

I can't imagine why. Every number is within +/- 25% of the actual caliber, additional numbers only indicate three or four different things, and there are typically no more than two or three different names for the same cartridge.

The prize he wins, of course, will be 4 dented cartridge cases, of such cartridges as the 7.92x57 JRS, the Volcanic, the Whitworth, and the .35 Sambar.

Yippee Ky Yiy!

 

[Otony]

Some pretty interesting information, but I need to point out that not only did the .44 American use a heeled bullet its case is NOT the parent of the .44 Russian, Special, or Magnum. It is actually a bit smaller in diameter, and to properly make cases for it nowadays requires the use of cut down and altered .41 Magnum brass.

Mike Venterino, for all his supposed faults, had an excellent article on the problems and issues involved making ammo for a .44 American. There is NO WAY one can utilize shortened or reformed Special (or Magnum) brass.

The American served as an insoiration for the Russian, but the case was also changed in the process, not just a switch to inside lubricated bullets.

 

[Jspotto]

I am studing this now. This can be endless and mind boggling, not to mention the WILDCATS!

 

[Pete D.]

more

And there's more...
"metric to caliber conversions"

Metric measurements are calibers. What we have discussed (among other things) are metric to inch conversions. 25.4mm = one inch.
That 25 ACP is 6.35mm or about one quarter of an inch.
Pete

 

[Black Butte]

45-70 - the 70 refers to the original blackpowder charge that it was loaded with...it is the same with the 30-30

Now we need to cover the tri-number convention, such as the .45-70-405 (.45 Government cartridge) or .45-70-500, where the last number indicates the grain weight of the bullet.

 

[pikid89]

my favorite is .17 Flintstone Super Eyebunger... .22-250 necked to .17 made by PO Ackley

 

[Gromky]

my favorite is .17 Flintstone Super Eyebunger... .22-250 necked to .17 made by PO Ackley

Nice. That even beats the .223 WSSM for silliness. Of course, you can just buy a rifle chambered in .223 WSSM...

 

[Jim Watson]

Then there is the British convention. A .450-400 is a .40 calibre, not .45. The parent case is given first, then the neckdown calibre.

 

[Pete D.]

more

A .450-400 is a .40 calibre, not .45.

Yep. I have a 577-450. But it really slugs out at .468 groove diameter and .458 across the lands (sorta, because Henry rifling is difficult to measure in either diameter.)
Pete

 

[bonza]

Yes, the British tend to use the bore diameter, rather than the grooves, that is why the .303 British actually uses .312" diameter bullets.

 

[9mmepiphany]

...and why they call the 7x57mm, a .276 Rigby

 

[VT Deer Hunter]

Heres one, my comp. rifle. 7.62x54 is .311 or .312 on cal. depending on the rifle slugging.

 

[JWF III]

Yes, the British tend to use the bore diameter, rather than the grooves, that is why the .303 British actually uses .312" diameter bullets.

Most European cartridges are land diameter, where as most American cartridges are groove diameter. (Not counting those cartridges that are neither diameter, as talked about earlier in this thread.)

One cartridge that differsis the 6.5x55 Swede is a groove diameter, while the 6.5 Carcano is land diameter (and requires a different bullet- .268" vs. the Swede's .264")

Japanese cartridges are groove diameter... 6.5 Jap is .264" and the 7.7 Jap actually uses the same diameter as the .303 Brit and the Russian 7.62s

Wyman

 

[Jim Watson]

And a .256 Newton is NOT a .25 caliber. That is bore diameter and groove/bullet is about .264" - 6.5 mm.

 

[revjen45]

Calibers are like English language spelling.
What does ghoti spell? Fish.
enouGH GH = F sound
wOmen O = short I sound
MoTIon TI = sh sound.
There are rules, sorta, and exceptions to every one.
.327 Mag bullet dia is .312. 7.62 NATO is .308. 7.82 Lazzeroni is .308.
Think I will invent a long magnum 7mm on .404 Jeffery case with a rebated rim and double shoulder (super secret interior ballistics) and call it the .299 Belchfire Magnum. You probably won't find ammo at Walmart.

 

[hiawatha]

There's the 7.62x54R, which, as others have mentioned, is .310-.312". But there's also the 7.62x53R, which is (usually) .308. It's the Finnish version. Think Lapua.

 

[sig220mw]

If the 25 caliber you are talking about is a rifle it is a .257 which in metric is actually 6.52 mm.