Why are gun calibres the sizes they are?
17 March 2004, 12:15 PM
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Why are gun calibres the sizes they are?
What is the origin of the seemingly random sizes of ammunition calibre?
Eg. .44, .22, 7.62mm 165mm etc.
I know where 12 and 10 bore sizes come from but the others have got me stumped.
Thanks
Steve
Eg. .44, .22, 7.62mm 165mm etc.
I know where 12 and 10 bore sizes come from but the others have got me stumped.
Thanks
Steve
17 March 2004, 12:22 PM
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I think many of them were fairly arbitrary. Weapon manufacturers specified their own calibres based on what they perceived was the best match with their rifling pattern and bullet length/diameter profile.
17 March 2004, 12:41 PM
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Not really I'm afraid! Smooth bore weapons were based on the number of ***** per lb and those calibres are now shotgun calibres. However when they came up with the bullet a lot of experimenting went on with its profile in order to retain as much kinetic energy whilst retaining stability to stop tumbling.
17 March 2004, 12:45 PM
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Originally Posted by Daz34
I think it is just down to conversion to the metric system 
e.g. the 7.62 is based on the winchester .308 and the 5.56 is based on the remmy .223
As I said above, there is no particular reason (that I know of!) for the original imperial calibres however, other than trial and error.
17 March 2004, 12:53 PM
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In the dim and distant past, the gunsmith was probably making a gun, grabbed the first drill bit that came to hand (DIY'er style) and said "that'll do". He'll have then carried on using the same size for other guns. The size has now stuck. 
John
John
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17 March 2004, 01:35 PM
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My understanding is that a calibre was originally decided from the desired weight of the bullet, in grains, and resulted from making the bullet an acceptable length to be easily handled. It was then standardised. Well, sort of.
For example, we used .303 while the Americans used .30 - not much of a difference but enough. Some calibres were simply decided on by the manufacturer, some by specific needs and some presumably by taking a convenient drill and making a hole before measuring it and saying "Ah yes - my .177 rifle..."
Big guns were a lot easier - either ignore the bore and describe it by shot weight, hence the 25 pounder, for example, or take 2", 3", 4" etc bores and then get the rough metric equivalent - 50mm 76mm and 100mm in this case...
SB
For example, we used .303 while the Americans used .30 - not much of a difference but enough. Some calibres were simply decided on by the manufacturer, some by specific needs and some presumably by taking a convenient drill and making a hole before measuring it and saying "Ah yes - my .177 rifle..."
Big guns were a lot easier - either ignore the bore and describe it by shot weight, hence the 25 pounder, for example, or take 2", 3", 4" etc bores and then get the rough metric equivalent - 50mm 76mm and 100mm in this case...
SB
17 March 2004, 02:52 PM
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The .38 special and .357 magnum are the same calibre.
They just have different case lengths.
The both have a case diameter of .38 and projectile diameter of .357
I could also mention how the 7.62mm calibre was adopted as the NATO standard but It would be to boring to read.
They just have different case lengths.
The both have a case diameter of .38 and projectile diameter of .357
I could also mention how the 7.62mm calibre was adopted as the NATO standard but It would be to boring to read.
17 March 2004, 07:03 PM
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So there is no good reason like the reson why the Saturn 5 rocket's size was the same size as a Roman chariot.
) there's a little piece of Internet wisdom that begs to differ:
Horse's ****!
The US standard railroad gauge (distance between the rails) is 4 feet 8.5 inches. That's an exceedingly odd number.
Why was that gauge used? Because that's the way they built them in England, and English expatriates built the US railroads.
Why did the English build them like that? Because the first rail lines were built by the same people who built the pre-railroad tramways, and that's the gauge they used.
Why did 'they' use that gauge then? Because the people who built the tramways used the same jigs and tools that they used for building wagons, which used that wheel spacing.
Okay! Why did the wagons have that particular odd wheel spacing? Well, if they tried to use any other spacing, the wagon wheels would break on some of the old, long distance roads in England, because that's the spacing of the wheel ruts.
So who built those old rutted roads? The first long distance roads in Europe (and England) were built by Imperial Rome for their legions. The roads have been used ever since. And the ruts? Roman war chariots first made the initial ruts, which everyone else had to match for fear of destroying their wagon wheels and wagons. Since the chariots were made for, or by Imperial Rome, they were all alike in the matter of wheel spacing.
Thus, we have the answer to the original question. The United States standard railroad gauge of 4 feet, 8.5 inches derives from the original specification for an Imperial Roman war chariot.
Specifications and bureaucracies live forever. So, the next time you are handed a specification and wonder which horse's rear came up with it, you may be exactly right. Because the Imperial Roman war chariots were made just wide enough to accommodate the back ends of two war-horses.
And now, the twist to the story...
There's an interesting extension to the story about railroad gauges and horses' behinds. When we see a Space Shuttle sitting on its launch pad, there are two big booster rockets attached to the sides of the main fuel tank. These are solid rocket boosters, or SRBs.
Thiokol makes the SRBs at their factory at Utah. The engineers who designed the SRBs might have preferred to make them a bit fatter, but the SRBs had to be shipped by train from the factory to the launch site. The railroad line from the factory had to run through a tunnel in the mountains. The SRBs had to fit through that tunnel. The tunnel is slightly wider than the railroad track, and the railroad track is about as wide as two horses behinds.
So, the major design feature of what is arguably the world's most advanced transportation system was determined by the width of a Horse's ****!
The US standard railroad gauge (distance between the rails) is 4 feet 8.5 inches. That's an exceedingly odd number.
Why was that gauge used? Because that's the way they built them in England, and English expatriates built the US railroads.
Why did the English build them like that? Because the first rail lines were built by the same people who built the pre-railroad tramways, and that's the gauge they used.
Why did 'they' use that gauge then? Because the people who built the tramways used the same jigs and tools that they used for building wagons, which used that wheel spacing.
Okay! Why did the wagons have that particular odd wheel spacing? Well, if they tried to use any other spacing, the wagon wheels would break on some of the old, long distance roads in England, because that's the spacing of the wheel ruts.
So who built those old rutted roads? The first long distance roads in Europe (and England) were built by Imperial Rome for their legions. The roads have been used ever since. And the ruts? Roman war chariots first made the initial ruts, which everyone else had to match for fear of destroying their wagon wheels and wagons. Since the chariots were made for, or by Imperial Rome, they were all alike in the matter of wheel spacing.
Thus, we have the answer to the original question. The United States standard railroad gauge of 4 feet, 8.5 inches derives from the original specification for an Imperial Roman war chariot.
Specifications and bureaucracies live forever. So, the next time you are handed a specification and wonder which horse's rear came up with it, you may be exactly right. Because the Imperial Roman war chariots were made just wide enough to accommodate the back ends of two war-horses.
And now, the twist to the story...
There's an interesting extension to the story about railroad gauges and horses' behinds. When we see a Space Shuttle sitting on its launch pad, there are two big booster rockets attached to the sides of the main fuel tank. These are solid rocket boosters, or SRBs.
Thiokol makes the SRBs at their factory at Utah. The engineers who designed the SRBs might have preferred to make them a bit fatter, but the SRBs had to be shipped by train from the factory to the launch site. The railroad line from the factory had to run through a tunnel in the mountains. The SRBs had to fit through that tunnel. The tunnel is slightly wider than the railroad track, and the railroad track is about as wide as two horses behinds.
So, the major design feature of what is arguably the world's most advanced transportation system was determined by the width of a Horse's ****!
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