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Metric and imperial calibres


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12 gauge. Gauged from a ball 12 to the 16 ounces. Wrongly called '12 bore'. (even 'tho I often use the term.)

 

.410" is a bore.*

 

* so will I be, if I keep putting folk right!

 

Not at all, I love all this trivia! Every day is a school day. However, it was my understanding that in regard to shotguns "gauge" is the US terminology and "bore" is the British? Certainly if you read any classic British textbook on the subject, such as WW Greener's "The Gun and its Development", they always refer to "bore", not "gauge". I understand the different way of designating the .410, would it be better to say, that .410 is a calibre and all others are bores (if you are British) or gauges (if you are from the US)? If a .410 was described using the system used for other shotguns, it would be a 68 bore/gauge.

 

As an aside, the reason such a system was used to measure gun barrels, was because very early gun makers did not always have access to bore measuring equipment which was sufficiently accurate, this being at a time when there was no such thing as standard screw threads, mass produced parts etc. However, they could access pure lead and use the appropriate sized balls of it as a reference when boring a gun. This was obviously not a precision measuring technique, but It was less critical with muzzle loaders where wads, ball moulds etc were bespoke for the gun. The same system was used for early muzzle loading artillery which were 6 pounders, 18 pounders etc. The terminology has remained, the Army still retain some 13 pounders and 25 pounders, primarily for saluting or ceremonial purposes.

Edited by Blunderbuss
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I used to teach volume and mass to my classes....wait for it......using 12 gauge/bore solid ball as an example. Based on a bore size of 0.729" and given the density of lead as 11.35 times the mass of the same volume of water, I asked them to find the mass of a solid ball.

 

I did this for years......and suddenly.....guess what?

 

'It has come to our notice that you are using firearms terms in your lessons. Please adopt another approach'

 

 

Did I obey? No!!!

Edited by Floating Chamber
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And I believe .38" is the nominal diameter of a loaded round of .38 Special, measured outside the cartridge case, not the diameter of the bullet (which is .357). I think there is some weird historical chain of events related to earlier cap and ball revolvers as to why that non-standard way of designating .38 Special came about.

 

It was related to older cartridges using outside lubed bullets of the same diametrer as the case like .22lr rounds do as opposeed to the inside lubes ones used today. They just used the same diameter case with a slightly smaller bullet. Not sure if it also had something to do with cap and ball revolvers but I wouldn't be surprised if it did.

 

J.

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12 gauge. Gauged from a ball 12 to the 16 ounces. Wrongly called '12 bore'. (even 'tho I often use the term.)

 

.410" is a bore.*

 

* so will I be, if I keep putting folk right!

 

12 gauge is definitely the correct terminology, rather than 12 bore. The latter term, as I've always understood, came about because of the way a gun makers order book would be laid out. There would be columns for the customer, type of gun, and such like and one relating to the calibre. It would be termed something like "Barrels bored for...." and the maker would write in 12, 28, 16, etc depending on what the customer ordered. Evenentually, the heading would simply be abbreviated to "bore" for quickness or to squeeze in extra lines.

 

J.

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You guys make me laugh...when ever I have pointed out the guage/bore terminology thingy most of you would shoot me down lol.

 

Another argument of mine is caliber is not just the bore...grooved or not but can also mean the chamber. 44mag for instance..429" bored/grooved barrel but we dont when asked what caliber it is say .429"....we say 44mag!

 

U.

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You guys make me laugh...when ever I have pointed out the guage/bore terminology thingy most of you would shoot me down lol.

 

Another argument of mine is caliber is not just the bore...grooved or not but can also mean the chamber. 44mag for instance..429" bored/grooved barrel but we dont when asked what caliber it is say .429"....we say 44mag!

 

U.

 

On another note. I have a 9mm rimfire shotgun but I can't seem to find any dimension on the actual cartridge which measures anywhwre near 9mm.

 

J.

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The bullet fired in a .243 is actually .236 of an inch or 6 mm

.243 is a caliber and not a bullet size, in the same way as .221, .222, .223, 22-250 etc are all .224 inch size bullets

 

Nope. It's definitely .243. .236 might be the bore diameter. Grove and bullet diameter is .243.

 

J.

i thoght it was the bore!

 

U.

 

Just measured mine. Seems to be .333 at the muzzle. Some way off 9mm which is .355.

 

J.

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Nope. It's definitely .243. .236 might be the bore diameter. Grove and bullet diameter is .243.

 

J.

 

Just measured mine. Seems to be .333 at the muzzle. Some way off 9mm which is .355.

 

J.

Choked maybe???

 

Yeah .243 is groove diameter....thats why 243Win is illegal for some deer in the British isles :lol: Law+ British=***!

 

U.

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Choked maybe???

 

Yeah .243 is groove diameter....thats why 243Win is illegal for some deer in the British isles :lol: Law+ British=***!

 

U.

 

It may be choked, doesn't look like it but it may be.

 

The diameter of a .243 bullet is .243, not .236. Bullets are sized to groove diameter.

 

J.

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I remember the law saying a rifle with a bore of .240 or greater etc. .243 Win has a bore less than .240.

The law does not say groove diameter!

 

Don't get me wrong...I don't give a monkeys! The experts tell me my 357mag aint strong enough for any deer! :lol: .

 

Another one is 6.5 swede....6.5mm and .264" bullets are actually close to 7mm, 6.75mm or so! And .270Win is more a 7mm than a 7mm Rem or Mauser!

 

U.

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I remember the law saying a rifle with a bore of .240 or greater etc. .243 Win has a bore less than .240.

The law does not say groove diameter!

 

Don't get me wrong...I don't give a monkeys! The experts tell me my 357mag aint strong enough for any deer! :lol: .

 

Another one is 6.5 swede....6.5mm and .264" bullets are actually close to 7mm, 6.75mm or so! And .270Win is more a 7mm than a 7mm Rem or Mauser!

 

U.

 

It's an interesting one. The Deer Act actually prohibits rifles with a 'calibre' less than .240". Calibre is not defined, I don't think.

 

J.

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It's an interesting one. The Deer Act actually prohibits rifles with a 'calibre' less than .240". Calibre is not defined, I don't think.

 

J.

I could of termed it wrong I guess then...thanks. I have however lost count of the discussions had about the term calibre.

Common to British calibre's was a general trend to go by bore size. Some most european and scandinavians prefered this also as opposed to American common practice to go with groove diameters.

I think the Americans have it right as knowing groove diameter is far more important to finding a correct fitting bullet over the bore dimension alone!

U.

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