Calibre designation versus bore diameter

[The Kurgan]

4mm .177" (.17 Rimfire)
5mm .204" (204 Ruger)
5.56mm .224" (22LR, 222/223 Rem, 5.56x45 NATO, 5.45x39)
6mm .243" (243 Win, 6mm Rem)
6.4mm .251" (25 ACP)
6.5mm .257" (25-06)
6.7mm .264" (6.5x55 SE, 260 Rem, 6.5 Creedmore)
7mm .277" (270 Win, 6.8 SPC)
7.2mm .284" (7X57 Mauser, 270 WSM, 7mm-08, 7mm Rem Mag, 280 Rem)
7.77mm .306" (7.5x55 Swiss)
7.8mm .308" (30-30, 308 Win, 7.62x51 NATO, 30-06, 300 Win Mag, 300 WSM)
7.9mm .312" (303 British, 7.62x25, 7.62x39, 7.62x54R, 32 S&W Long, 32 H&R Mag, 327 Federal Mag)
7.94mm .3125" (32-20, 32 ACP)
8mm .315" (310 Cadet, 7.5mm Swiss Ordnance)
8.16mm .321" (32 Win Special, 7.92x33 Kurz)
8.23mm .323" (8x57 Mauser, 325 WSM, 8mm French Ordnance)
8.3mm .327" (8mm Lebel)

Clearly, calibre designation is not always the best indicator of bore size, complicated further by whether measurements are taken at the grooves or lands.

 

[The Kurgan]

8.6mm .338" (338 Lapua, 338-06)
9mm .355" (38 Special, 357 Mag, 9x19)
9.1mm .358" (35 Rem, 35 Whelen, 358 Win, 358 Norma mag, 350 Rem Mag)
9.3mm .366" (9.3x74R)
10mm .400" (40 S&W, 10mm Auto)
10.7mm .423" (404 Jeffery)
10.9mm .429" (444 Marlin, 44 Mag)
11.43mm .450" (45 ACP, 454 Casull, 45 Long Colt, 455 Webley)
11.63mm .458" (45-70, 450 Marlin)

 

[nowarningshot]

Particularly true with pistol calibers.... .429. 38 special and 357 mag. Then there is the 404 Jeffrey, which is not .404, but .423 i believe. Further complicating this, add some of the military calibers were actual bore varies year to year and by manufacturer.......303 British is of course not .303, supposed to be .311, but can be anywhere fom .308 to .314. Seems to be a trend towards less of this if you discount confusing proprietary calibers.....Lazzoroni.....Weatherby.

 

[tjhaile]

A lot of the confusion is in using land versus groove diameter. Most metric designations use land diameter, which is why, for example, 7mm bullets are actually 7.21mm (.284").

Many older inch designations use the land diameter convention as well. This is why .30 calibre is really .308", .303 is .311", or 270 is .277".

 

[guntech]

Confusing terms... caliber, cartridge designation, metric designations...

It doesn't help when we are incorrectly taught... for instance the Canadian Firearms Course uses caliber and cartridge designation interchangeably and the RCMP use 'caliber' to describe cartridge designation. They are two separate terms commonly misused.

Caliber designation is quite simple. Correctly used it is in reference to the barrel and caliber is always measured in thousands of an inch. .30 caliber is exactly .300" and it is the bore size of the barrel. A bullet designed to be shot in a .30 caliber barrel measures .308" to fit the groove size of a .30 caliber barrel.

So the caliber of a barrel is the bore diameter and the bore diameter is measured top of land to top of land, not groove to groove which is bullet diameter.

Cartridge designation is very confusing and ends up being simple memorization. There is no fixed rule when it comes to naming a cartridge.

So when someone asks you what caliber do you shoot, they probably should be asking you what cartridge you shoot.

Referring to the barrel stamp is more reliable than stating a caliber.

 

[tootall]

4mm .177" (.17 Rimfire, airgun pellets)
5mm .204" (204 Ruger)
5.56mm .224" (22LR, 222/223 Rem, 5.56x45 NATO, 5.45x39)
6mm .243" (243 Win, 6mm Rem)
6.4mm .251" (25 ACP)
6.5mm .257" (25-06)
6.7mm .264" (6.5x55 SE, 260 Rem, 6.5 Creedmore)
7mm .277" (270 Win, 6.8 SPC)
7.2mm .284" (7X57 Mauser, 7mm-08, 7mm Rem Mag, 280 Rem)
7.77mm .306" (7.5x55 Swiss)
7.8mm .308" (30-30, 308 Win, 7.62x51 NATO, 30-06, 300 Win Mag)
7.9mm .312" (303 British, 7.62x25, 7.62x39, 7.62x54R, 32 S&W Long, 32 H&R Mag, 327 Federal Mag)
7.94mm .3125" (32-20, 32 ACP)
8mm .315" (310 Cadet, 7.5mm Swiss Ordnance)
8.16mm .321" (32 Win Special, 7.92x33 Kurz)
8.23mm .323" (8x57 Mauser, 325 WSM, 8mm French Ordnance)
8.3mm .327" (8mm Lebel)

Clearly, calibre designation is not always the best indicator of bore size, complicated further by whether measurements are taken at the grooves or lands.

.177 airgun is 4.5mm

 

[guntech]

A lot of the confusion is in using land versus groove diameter. Most metric designations use land diameter, which is why, for example, 7mm bullets are actually 7.21mm (.284").

Many older inch designations use the land diameter convention as well. This is why .30 calibre is really .308", .303 is .311", or 270 is .277".

No, no, no

.30 caliber is .300" and uses .308" diameter bullets.

Caliber is always expressed in thousands of an inch and always refers to bore diameter not groove diameter. Don't confuse cartridge designation or bullet diameter with caliber.

 

[The Kurgan]

yes, you are correct...

 

[tjhaile]

No, no, no

.30 caliber is .300" and uses .308" diameter bullets.

Caliber is always expressed in thousands of an inch and always refers to bore diameter not groove diameter. Don't confuse cartridge designation or bullet diameter with caliber.

Oxford English Dictionary begs to differ:

2. The internal diameter or bore of a gun barrel [land and groove diameters are both internal diameters]
2.1. The diameter of a bullet, shell, or rocket.
2.2. The diameter of a body of circular section, such as a tube, blood vessel, or fibre.

http://www.oxforddictionaries.com/definition/english/calibre

 

[medvedqc]

No, no, no

.30 caliber is .300" and uses .308" diameter bullets.

Caliber is always expressed in thousands of an inch and always refers to bore diameter not groove diameter. Don't confuse cartridge designation or bullet diameter with caliber.

try to explain that to an european guy: a 7x64 is a 7mm lol ....

 

[tokguy]

I'm of the opinion that it is like a trade name, what to do to differentiate your offering from other manufacturers? Well a different name and / or designation is an idea, whether it matches the caliber exactly or not.
I'm supposing here, but it was assumed that a reloader had to know what caliber of bullets to use, or...well ' Mother Nature would vaccum out the shallow end if the gene pool 'as she often does. Litigation used to be a little tougher to accomplish in the begone days perhaps?

 

[Grizzly Adams]

I'm of the opinion that it is like a trade name, what to do to differentiate your offering from other manufacturers? Well a different name and / or designation is an idea, whether it matches the caliber exactly or not.
I'm supposing here, but it was assumed that a reloader had to know what caliber of bullets to use, or...well ' Mother Nature would vaccum out the shallow end if the gene pool 'as she often does. Litigation used to be a little tougher to accomplish in the begone days perhaps?

.340 Weatherby actually uses.338 bullets , .460 is 458, all in the name of Marketing.

Grizz

 

[porpoise]

A lot of the confusion is in using land versus groove diameter. Most metric designations use land diameter, which is why, for example, 7mm bullets are actually 7.21mm (.284").

Many older inch designations use the land diameter convention as well. This is why .30 calibre is really .308", .303 is .311", or 270 is .277".

No, 30 cal is 300, 303 is 303 and 270 is 270