Thread: Caliber names

So, the .303 caliber is actually .311" in size. But the .308 caliber is actually .308" in size. However, .308 is also called "7.62 NATO" despite .308" being 7.8mm. Also, "7.62x39" (which may pre-date 7.62 NATO?) is actually .311". 7.62mm is 0.300".



The .223 caliber is actually .224", or 5.68mm, but it's also called the "5.56 NATO". .224 and .220 are also .224", as is anything called ".22", but .222 (which used to be .222") is .223". 5.56mm is actually around .219", so who knows where that came from.



The 6.5mm caliber is .264", despite 6.5mm being .255" (While the ".25" family clock in at .257".)

7mm is actually .284" which is somewhere around 7.2mm, but maybe that's just lazy rounding.

I'm aware that this is mostly a series of historical accidents and "near enoughs", but did nobody ever stop and think "this is getting a bit out of hand, perhaps we need to rethink our naming system"?

Now that's heavy! The .45 cal I size to .41 and the .577 I size to .571 and the .55 I use a .53 ball wrapped in onion paper, so it all started long long ago

7.62mm groove, 7.8mm land = .308.

Etc.

It's to do with land/groove diameters for most of these

And using lead as I do it bumps up and fits the bore

Talk to women about clothes sizing - now there's a completely inconsistent nightmare

I thought most modern calibers came after the 30/06 named because it was 30cal designed in 1906... 30/06. The 308 was a shortened version of the 30/06 I cannot remeber how the 08 came into it but I thaught it was a measurement thing. Most names came from the designers/wildcatters looking for a catchy name and have little to do with exact bore size. This was my understanding which may be partly right or not at all. Wheres flintlock when you need him.

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.308" is the groove diameter, 7.82mm. .300 or 7.62mm is the land diameter.

So e.g. .223: 5.56mm = .219", .224" diameter = .005" groove depth.

.308 vs .300 = .008" groove depth. (.303 vs .311 = also .008" groove depth? But it's named for the smaller not the larger.)

6.5mm = .255", so .264 - .255 = .009" groove depth.

And so on, I guess. So, interestingly, where there's a mm-united caliber name (5.56, 6.5, 7, 7.62), that usually seems to refer to the smaller dimension, and the corresponding imperial measure (.223, .284, .308) seems to refer to the outer dimension. Is that just accidental, or something the euros and americans do differently?

With the older rifles you need to slug the barrel to get the dimensions, an difficult to measure uneven number of rifling grooves. Older barrel can vary

Originally Posted by Maca49

With the older rifles you need to slug the barrel to get the dimensions, an difficult to measure uneven number of rifling grooves. Older barrel can vary

Also on new ones that don't have the calibre/chamber designation engraved on the barrel......

Huh, interesting. It is something I like about guns (my day job is computers) is just how lo-fi the tech really is. Sure, my 25-06 may not be the "best" caliber, but hell, a 1906 cartridge design is still doing pretty well, that's quite something.

My 6-year old laptop is obsolete, my 106-year old cartridge still has off-the-shelf ammo and rifles for it, and apart from the noise, barrel length, short barrel life, and poor projectile selection , competes reasonably well.

Originally Posted by mattdw

Huh, interesting. It is something I like about guns (my day job is computers) is just how lo-fi the tech really is. Sure, my 25-06 may not be the "best" caliber, but hell, a 1906 cartridge design is still doing pretty well, that's quite something.

My 6-year old laptop is obsolete, my 106-year old cartridge still has off-the-shelf ammo and rifles for it, and apart from the noise, barrel length, short barrel life, and poor projectile selection , competes reasonably well.

117g ballistic tips or 115g vld projectiles would bring your 2506 right up there with the best of them

'my 106-year old cartridge still has off-the-shelf ammo and rifles for it, and apart from the noise, barrel length, short barrel life'


Hi guys, excuse my ignorance, if im reading the above statement from mattdw correctly, does 25-06 cal 'burn barrels' quickly with factory ammo?....as i have one!

Scouser, my understanding is, yes, relatively so. I'm running warm handloads, and can expect somewhere around a thousand rounds before accuracy starts to fade, I think. Factory ammo would presumably be a little better if it's not running as hot. (I could be wrong on this.)

Originally Posted by Tussock

Its all relative. Depends on your definition of quickly. If you fire hundreds and thousands of rounds then yes. If you fire 20 a year then no.

But yes, compared to other rounds they tear into barrels, as they are quite overbore. The barrel I took off my older Ruger 25-06 was visibly obliterated.

The poo for free is suprising hard on barrels for a factory round especially if you use them for what they are best at, ventilating heaps of Goats in a hurry.....