Metric to caliber conversion


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pwillie
January 30, 2011, 07:55 PM
What is a 25 caliber in metric terms?:banghead:

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Ian
January 30, 2011, 08:09 PM
6.35mm. The conversion is 25.4mm per inch.

Ruger GP100 fan
January 30, 2011, 08:10 PM
Multiply by 25.4.

Ruger GP100 fan
January 30, 2011, 08:11 PM
6.35mm. The conversion is 25.4mm per inch.
I gotta learn to type faster.

bigfatdave
January 30, 2011, 08:30 PM
The .25 ACP (Automatic Colt Pistol) (6.35x16mmSR) centerfire pistol cartridge is a semi-rimmed, straight-walled pistol cartridge introduced by John Browning in 1905 alongside the Fabrique Nationale model 1905 pistol.

From Wikipedia:
http://en.wikipedia.org/wiki/.25_ACP

This stuff isn't hard to look up in the information age, particularly cartridge info.

But if you just want a conversion, plug it into google as {number} {units you have} in {units you want} ... example: "0.25 inches in millimeters"
http://www.google.com/search?q=0.25+inches+in+millimeters
or "1200 feet per second in meters per second"
http://www.google.com/search?q=0.25+inches+in+millimeters#sclient=psy&hl=en&q=1200+feet+per+second+in+meters+per+second&fp=dded8f20a6bb9442

I have a few handy reference charts for manual conversion, and I have a few basic conversions in my own head, but I'm spoiled by google ever since they started letting you do calculations in the regular search bar.

pwillie
January 31, 2011, 06:07 AM
Thanks all,....so my 25 caliber is 6.35 mm?

vaupet
January 31, 2011, 07:13 AM
Caution: an inch is always 25.4 mm
a 7.62 mm is always a 7.62 mm
but a XX caliber is not always 0.XX inch (for instance: 38 special and 357 magnum = same diameter)

greetings

Peter

PapaG
January 31, 2011, 10:05 AM
And a 44 is really a 43 (.429 or .430) and a 44 cap and ball is a 45 (451 normally) and a 30-30, a 308, a 30-06, a 7.62, a 300, are all really .308 dia.

Do we dare get into what the second number "might" mean.....45-70, 30-06, 30-30, 38-40, 7.62 X 51 and so on....

rambler
January 31, 2011, 10:18 AM
Do we dare get into what the second number "might" mean.....45-70, 30-06, 30-30, 38-40, 7.62 X 51 and so on....

YES!

Also, why is 380 called 380?

M2 Carbine
January 31, 2011, 10:33 AM
Also, why is 380 called 380?
Because it's .355 diameter, like the 9mm, and someone didn't want to call it 9mm.

and a .223 bullet is actually.224 diameter.

and a 9x18 Makarov bullet can be .363, .364 or.365 diameter.

Confusing ain't it?:)

Jim Watson
January 31, 2011, 10:40 AM
Your .25 caliber WHAT?

6.35mm = .250"
A .25 ACP bullet is typically .251", pretty close.
But a .25-06 rifle bullet is .257" which is 6.53mm. But it will be cataloged as a 6.35mm in Europe because the BORE diameter is about .250".

pwillie
January 31, 2011, 11:00 AM
So,a 25 06 and a 257 is the same? Is this how Weatherby came up with a 257 Weatherby?:scrutiny:

Gromky
January 31, 2011, 11:24 AM
rambler the second number can indicate several things. For the .30-06 the 06 is when it was brought into use by the army. For the .30-30 the 30 is the original powder load. And when it's something like 7.62x51mm the 51mm is case length. Nice and standardized, right?

I think a lot of it is differentiation on the market. When you come up with your new round you want it to stand out on the market, one easy way to do it is to go with a number that's different from your competitors. Otherwise you have to name it after your company, add an improved, or make sure there's magnum in the title.

Smokey Joe
January 31, 2011, 11:30 AM
P Wille, is that THERE IS NO BASIC RULE!!

When you design a new cartridge, you can call it whatever you want. Usually, marketing possibilities are a factor.

In strictly measurement terms, 1.00 inches = 2.54 cm or 25.4 mm. That can be used as a conversion factor, but it may or may not tell you anything true about the diameter of the bullet for a particular cartridge.

My favorite marketing example is the .250-3000, which was marketed as such back when 3000 fps in a standard commercial rifle cartridge was a big deal. The same cartridge is now sold as the .250 Savage, since 3000 fps is no longer a big deal.

You can call your new cartridge something easy-to-remember, like .38 Special (which started out as the .38 Smith & Wesson Special!) or name it after the actual bore diameter, like .357 Magnum, which sounds ominous but is actually the same bore as the .38 Spl.

The military in the US has its own cartridge designations, which get transmogrified into commercial designations for the same cartridge when that cartridge goes commercial , as in .30-'06, which was a design change from the earlier .30-'03.

And so on. Any cartridge collector, or firearms historian (neither of which designations fits me) can probably supply a dozen more examples without straining.

For us ordinary blokes, the thing to do is to know for sure, the current and past name(s) of the cartridge we want to use in our firearm, and when handloading, know exactly what diameter bullet is proper to use.

But as for rhyme or reason in the names of cartridges, well, there ain't much.

9mmepiphany
January 31, 2011, 03:39 PM
Do we dare get into what the second number "might" mean.....45-70, 30-06, 30-30, 38-40, 7.62 X 51 and so on....

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

30-06 (30'06) - as already mentioned, the second number refers to the year it was adopted for military service. However, 25-06, 7mm-06, 8mm-06, refer to the parent cartridge which was necked down/up to produce a newer cartridge (most started as wildcat cartridges)

7.62x51 (actually 7.62x51mm)- is a metric designation and usually more accurate and informative as it gives both the diameter of the projectile and the length of the casing. That's how you know the M14 round (7.62x51mm) is longer than the AK-47 round (7.62x39mm) or that a 9mm (9x19mm) is longer than a .380 (9x17mm)

One of my favorite trivia cartridges is the 38-40. It shoots a .401 diameter bullet. ah, you say...that's the second number. No, that 40 still refers to the original blackpowder charge

at least the .44 spl/mag being .429" make sense. The .44 American, parent to the .44 Russian and .44 Spl was originally loaded with a heeled bullet , like a .22lr, and was the same diameter as the case. When they loaded non-heeled bullets for the calibre, they had to be reduced in diameter to fit into the case

hirundo82
January 31, 2011, 03:47 PM
a 30-30, a 308, a 30-06, a 7.62, a 300, are all really .308 dia.

Except for when it is .312 (http://en.wikipedia.org/wiki/7.62x39) or .295 (http://en.wikipedia.org/wiki/7.62x38R).

hirundo82
January 31, 2011, 03:55 PM
at least the .44 spl/mag being .429" make sense. The .44 spl was originally loaded with a heeled bullet , like a .22lr, and was the same diameter as the case. When the loaded non-heeled bullets for the calibre, they had to be reduced in diameter to fit into the case

IIRC neither .44 Special nor its parent round .44 Russian ever used a heeled bullet. However, their predecessor the .44 S&W American did, and the designation stuck for its descendents, later including the .44 mag.

oneounceload
January 31, 2011, 03:59 PM
So,a 25 06 and a 257 is the same? Is this how Weatherby came up with a 257 Weatherby

The diameter bullet both cartridges use is the same - the cartridges themselves, however are not.

IMO, metric is MUCH easier as the numbers applied are true to the diameter and case in the majority of instances

exeagle
January 31, 2011, 04:09 PM
Some good info in this thread....caliber designations have always confused the heck out of me. :confused:

Cosmik de Bris
January 31, 2011, 04:24 PM
...and it depends whether you measure the bullet, the distance between the rifling grooves, or the distance between the rifling lands.

9mmepiphany
January 31, 2011, 04:56 PM
IIRC neither .44 Special nor its parent round .44 Russian ever used a heeled bullet. However, their predecessor the .44 S&W American did, and the designation stuck for its descendents, later including the .44 mag.

You're right...brain fade time...the .44 S&W American is the culprit with the heeled bullet...I edited my post

Gromky
January 31, 2011, 11:49 PM
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.

To be honest, outside of the easy groups (like .30 cal rifles...as long as you recognize .308 vs. .311/312), I don't think there's any way to figure it out except experience and research. Even for .30 you have to know that .308 is the same as .300 Savage/Win Mag/etc. It's easy to research for what you own, but you can't count on anything you don't know making sense.

Jim Watson
February 1, 2011, 01:00 AM
and it depends whether you measure the bullet, the distance between the rifling grooves, or the distance between the rifling lands.

Or it depends on whether somebody else has already used a number that is an actual measurement of something about the gun or ammo and your advertising department has to come up with something catchy.

My favorite example of how shooters count:
.218 Bee, .219 Zipper, .220 Swift, .221 Fireball, .222 Remington, .223 Remington, .224 Weatherby, and .225 Winchester ALL shoot .224" diameter bullets.
But .22 Remington Jet and .22 Savage High Power do not.

pikid89
February 1, 2011, 02:54 AM
45-70 - the 70 refers to the original blackpowder charge that it was loaded with...it is the same with the 30-30

your right on the 45-70 and 70gr of BP,
but the .30-30 was designed for smokeless powder and its actual designed name was .30 WCF or .30 winchester center fire, for use in the Winchester model 1894 rifle.
Competitors, Marlin and UMC, did not want to put rival winchester's name on their guns and ammo, and used the name .30-30, the -30 referring to the original load of early smokeless powder. (According to wiki, that is equivalent to IMR 4064)....and it stuck

pikid89
February 1, 2011, 03:00 AM
45-70 - the 70 refers to the original blackpowder charge that it was loaded with...it is the same with the 30-30

your right on the 45-70 and 70gr of BP,
but the .30-30 was designed for smokeless powder and its actual designed name was .30 WCF or .30 winchester center fire, for use in the Winchester model 1894 rifle.
Competitors, Marlin and UMC, did not want to put rival winchester's name on their guns and ammo, and used the name .30-30, the -30 referring to the original load of early smokeless powder. (According to wiki, that is equivalent to IMR 4064)....and it stuck

Smokey Joe
February 1, 2011, 11:09 AM
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
February 1, 2011, 12:32 PM
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
February 1, 2011, 01:32 PM
I am studing this now. This can be endless and mind boggling, not to mention the WILDCATS!

Pete D.
February 1, 2011, 10:16 PM
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
February 1, 2011, 10:27 PM
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
February 1, 2011, 10:29 PM
my favorite is .17 Flintstone Super Eyebunger... .22-250 necked to .17 made by PO Ackley

Gromky
February 1, 2011, 10:51 PM
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
February 2, 2011, 03:14 PM
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.
February 2, 2011, 04:24 PM
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
February 2, 2011, 06:19 PM
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
February 2, 2011, 07:00 PM
...and why they call the 7x57mm, a .276 Rigby

VT Deer Hunter
February 2, 2011, 07:14 PM
Heres one, my comp. rifle. 7.62x54 is .311 or .312 on cal. depending on the rifle slugging.

JWF III
February 2, 2011, 07:39 PM
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
February 2, 2011, 08:00 PM
And a .256 Newton is NOT a .25 caliber. That is bore diameter and groove/bullet is about .264" - 6.5 mm.

revjen45
February 2, 2011, 08:46 PM
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
February 3, 2011, 12:01 AM
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
February 3, 2011, 01:08 AM
If the 25 caliber you are talking about is a rifle it is a .257 which in metric is actually 6.52 mm.

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