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2007-04-15 18:24:42
The_Mac
Member
+96|6676
I hear people say, "30 cal or 50 cal machine guns" and the caliber of this gun is 7.62mm. But what is the Calibre vs. mm. I know they're both measurement of diameter of the barrel, but what are the conversion factors.
Or does a 30 cal. = a 30mm?
I have had this question for ages, so if you could help me out, I'd appreciate it. (+1 karma to whoever answers it)
2007-04-15 18:26:18
ThaReaper
Banned
+410|7090
I don't even know what cal. means either.
2007-04-15 18:27:35
Teebaggs1
X-LG Member
+25|7201|Maine, MA, and PJ concerts
http://en.wikipedia.org/wiki/Caliber
2007-04-15 18:29:21
nukchebi0
Пушкин, наше всё
+387|6775|New Haven, CT
To summarize:

If it is caliber, such as .30 cal, then the barrel has a diameter of 3/10 of an inch. If it is in mm, then the diameter is mm.
2007-04-15 18:29:22
Doctor Strangelove
Real Battlefield Veterinarian.
+1,758|6919
Calibre, as in the unit measures the with of the bullet in inches. MM is the with in Milimeters. Calibre also can refer to the size of a round, no specific measurement.
2007-04-15 19:00:54
Skorpy-chan
Member
+127|6796|Twyford, UK
Caliber as applied to rounds is the diameter of the round in inches, or more commonly fractions thereof. If it's in mm, then it's the diameter of the round in millimeters.

A handy guide off the top of my head:
5.56mm -> .223
7.62mm -> .3 or .303
12.7mm -> .50 cal.
2007-04-15 19:02:33
Havok
Nymphomaniac Treatment Specialist
+302|7126|Florida, United States

Skorpy-chan wrote:

Caliber as applied to rounds is the diameter of the round in inches, or more commonly fractions thereof. If it's in mm, then it's the diameter of the round in millimeters.

A handy guide off the top of my head:
5.56mm -> .223
7.62mm -> .3 or .303
12.7mm -> .50 cal.
That's a helpful chart. +1
2007-04-15 19:05:13
The_Mac
Member
+96|6676

Teebaggs1 wrote:

http://en.wikipedia.org/wiki/Caliber
I know, but it just confused the hell out of me even more.

Alright, I understand it better, essentially, they're separate from each other in terms of conversion...or are they? So how would convert calibre (measurement) to mm? is there some sort of math?
Thanks all.

Last edited by The_Mac (2007-04-15 19:07:46)

2007-04-15 19:12:13
imortal
Member
+240|7116|Austin, TX
The calibre of a firearm is the measurement of the bore of the barrel.  In other words, the measurement of the opening that the bullet comes out. 

Calibre is measured in three ways.  Inches, millimeters, and guage.  Inches and mm are pretty simple to understand.  Guage is a lot harder; the smaller the guage, the bigger the opening.

Converting inches to mm is pretty fun, but straight forward.  However, there is more to power than just calibre.  a 7.65mm pistol has nowhere near the power of a 7.62mm rifle. 

And bullet weight is measured in grains.  If memory serves (and nothing says it does) I think a grain is about 60mg.

inches to mm.  1 inch=25.2mm   So, a .50 calibre round is 12.6mm.  Of course, calibres have often been rounded, so the measurements may not be exact.  A .38 special bullet can ber fired out of a revolver designed to fire .357 magnum rounds.

Last edited by imortal (2007-04-15 19:14:30)

2007-04-15 19:13:32
globefish23
sophisticated slacker
+334|6774|Graz, Austria
It's actually very simple.
In the English language the leading zero in numbers smaller than 1 is left out.
Caliber .30 means 0.3 inch, which is 0.762 centimeters or 7.62 millimeters.
(The conversion factor of inch <> cm is 2.54.)
2007-04-15 19:14:09
Reciprocity
Member
+721|7031|the dank(super) side of Oregon
how can you be confused?  the caliber or calibre of a bullet is simply the diameter.  metric or elglish stantard/fractional.  a bullet with a diameter of 7.62mm is roughly equivolent to a bullet with the diameter of .3 inches or 3/10 of an inch.  comprende?
2007-04-15 19:17:36
GunSlinger OIF II
Banned.
+1,860|7094

rdx-fx wrote:

Quick and dirty guide to bullet measurements;

.22 caliber = .223" diameter = 5.56mm diameter (example .223 Remington = 5.56mm NATO)
.30 caliber = .308" diameter = 7.62mm diameter (example .308 Winchester = 7.62mm NATO)
.50 caliber = .500" diameter = 12.7mm diameter (example .50 BMG = 12.7mm)

A few things to keep in mind;
The Bullet is the part that goes flying.
The Cartridge is the case+powder+bullet+primer.. the thingy you load into the rifle.

Also,
Just because a round is stated as a "7.62mm" or a ".22 cal", doesn't mean that they're the same.
The M-16 fires the 5.56mm NATO round, which is the same caliber as the .22 Long Rifle - but they have vastly different bullet weights (from the length), and vastly different amounts of gunpowder propelling them.

A more subtle difference;
AK-47 uses the 7.62x39 cartridge, M-60 and M-240 use the 7.62x51. NOT the same round at all.
The first number (7.62mm) describes the bullet diameter,
the second number describes the length of the case (39mm and 51mm, respectively)
Generally, the larger the second number, the more powder in the case - and the more energy to the bullet.

Also;
Though a bullet design may claim to be a ".30 caliber", there is a bit of variation in the actual diameter of the bullets between different cartridges.  Could be .302, .306, but usually .308.  It's more useful to think of "xx caliber" as a general guideline or family of rounds, rather than an engineering measurement.
lies
2007-04-15 19:22:12
GunSlinger OIF II
Banned.
+1,860|7094
what about my bushmaster?
https://upload.wikimedia.org/wikipedia/en/5/5b/M242-1.jpg

Last edited by GunSlinger OIF II (2007-04-15 19:24:50)

2007-04-15 19:45:57
Skorpy-chan
Member
+127|6796|Twyford, UK
25mm, not given in caliber due to the NATO standardisation making everything metric.

Of course, to confuse things even more, caliber is also used to measure the length of the gun barrel itself. I don't remember how that's determined, so I stick with the more rememberable way of the length in inches.
Or feet for larger weapons, such as the GAU-8.

Another useful thing is RPM (rounds per minute) which is exactly as it says on the tin; the number of rounds the weapon spews out every minute. Now commonly given in multiple values for each weapon due to trigger groupings (small arms), preset speeds (gatling guns, revolver cannons and chainguns), or simply differing conditions (crew-served weapons such as artillery pieces or tank cannons; generally burst and sustained rates).

 

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