Question : Calibres Explained

Meclor

Could someone explain or point me to a link that explains the correlation between calibre descriptions


For example, how does .22, .220. 223 .308 equate to 9mm, 5.56m and 7.62 etc.

I don't really understand what .22 describes in terms of size. Is it the dimensions of the cartridge? and what does 6mm and 9mm mean, again I understand i describes the size of the cartridge in some way but how do the 2 methods of describing the cartridge correlate with one another?

Rovi

You're not in the Ballistics Section at Garda Headquarters by any chance, are you ?



Sorry Meclor, I couldn't resist

I'll get back later if no-one else answers you.

.

Pigman II

http://en.wikipedia.org/wiki/Caliber

Meclor

LOL, I am in fact consultant for them, they have come in with a query relating to new legislation and I was hoping the magic internet could tell me. Cause I don't have a bullies. The internet I have on CD at home wasn't much use:D

jaycee

Not absolutely accurate , but a handy "Rule of thumb" is..

If the calibre is expressed as .. .22 for example
it refers to a measurement as divisions of an inch (25.4mm)

.25 is one quarter of an inch therefore it would be about 6.35mm in width.
And so on for the differnt calibres.

Calibres expressed in Milimeters ..eg 9mm , are exactly that 9mm in width.

An ordinary .22 rifle bullet equates to 5.56mm
The much mentioned and unjustly maligned .308 = 7.62mm

Simple subtraction then shows that

............7.62--(.308)
Minus.....5.56--(Plain 'ol .22)

---

Equals....2.06 mm in the difference
Or a radius of just over a Millimeter in the difference .

Not as deadly as it sounds ..is it.

Traumadoc

Just to make things complicated : Why is a 270 actually .277 or a .303 actually .310?

Rovi

There's a lot of good info here- http://www.quarry.nildram.co.uk/Cartridges.htm.
The first section, 'What are cartridges and how are they described?,' covers what you're asking about.

To summarize a line from Chapter 1 of Cartridges of the World-
"Cartridge nomenclature isn't so much a system as a code, and it is neither accurate nor consistent"

We're dealing with a system of weights and measurements that has evolved over hundreds of years, with all the quirks and idiosyncrasies this implies.
Manufacturer's advertising departments also like to 'sexify' cartridge names by rounding actual calibres off to easier to remember numbers, and 'cool' names aren't unheard of either. .577 Tyrannosaur, anyone?

Some common calibres-
.22-250 Remington
Actual bullet diameter- .224 inch.
The name comes from the nominal bullet calibre (.22), and the first part of the name of the cartridge from which it was developed, the .250-3000 Savage.
The .250-3000 Savage itself (actual bullet diameter- .248 inch) was introduced in 1915 by the Savage Arms Company. It's name is derived from it's nominal calibre (.250) and it's (reputed) muzzle velocity- 3000 feet per second.

.25-06 Remington
Actual bullet diameter- .257 inch.
Developed from the .30-06 Springfield, with the neck of the shell closed down to the smaller bullet. The .30-06 (actual bullet diameter- .308 inch) gets the '06' part of it's name from the year it was introduced- 1906.

Here's a great one-
.30-30 Winchester
Actual bullet diameter- .308 inch.
The first bit's easy enough, but the second '30?'
That's the quantity (in grains) of powder that went in the case when it was developed in 1895! This naming convention (bullet calibre + powder load) was how it was done in the early days of metallic cases when they were filled with blackpowder.

European (Metric) sizes are much easier to deal with, as they are pretty much 'what it says on the tin.'
EXCEPT that bullet calibre is usually expressed as the diameter of the 'lands' (the top part) of the rifling of the barrel for which the bullet is intended. Imperial bullets are usually expressed as the diameter of the bottom of the grooves of the rifling of the barrel for which the bullet is intended.
<sigh>
Stuff about rifling here- http://en.wikipedia.org/wiki/Rifled.

So, we get this sort of thing-
7.62x51mm NATO
Actual bullet diameter- 7.82mm.
The 51mm refers to the case length.
This round is identical to the .308 Winchester.
7.82mm = .308 inch

The same sort of thing occurs with the 5.56x45mm NATO.
Actual bullet diameter- 5.69mm.
The 45mm refers to the case length.
This round is (almost) identical to the .223 Remington.
5.69mm = .224 inch

Why is the .223 Remington called that when its actual calibre is .224 inch?
I have no idea. It's late and my head hurts from all this stuff, and I'm off to bed.

.

Clare gunner

Meclor wrote:

LOL, I am in fact consultant for them, they have come in with a query relating to new legislation and I was hoping the magic internet could tell me. Cause I don't have a bullies. The internet I have on CD at home wasn't much use:D

If you dont mind me asking;what do you consult for them,and why is the people who should be most in the know about balistics and calibres and pending legislation,consulting a "civvie"???
Just very curious

Sparks

Excellent summary CG!

Meclor

Thanks for all the good info,

It'll take me a while to get me head aorund that, well remember it anyway.

P.S, I don't consult for the John Law. I barely know the business end of a broom stick, never mind a boom stick.:eek:

Clare gunner

The same sort of thing occurs with the 5.56x45mm NATO.
Actual bullet diameter- 5.69mm.
The 45mm refers to the case length.
This round is (almost) identical to the .223 Remington.
5.69mm = .224 inch

Why is the .223 Remington called that when its actual calibre is .224 inch?
I have no idea. It's late and my head hurts from all this stuff, and I'm off to bed.

Methinks,it has somthing to do with differanting between the civillan 223 and the milspec 5.56,and somone not doing their sums right and political messing about between Washington DC and NATO in the 60s.Or somthin on those lines.

jeffshc1

That's the quantity (in grains) of powder that went in the case when it was developed in 1895! This naming convention (bullet calibre + powder load) was how it was done in the early days of metallic cases when they were filled with blackpowder.

Hence the 45/70 and so on.
Wouldn’t you love to see some geezer in the old west trying metric?!?

Hey Festus, how mainy leeters a powdeer is in a haf a pound?