View Full Version : Origin of bullet diameter?
June 6, 1999, 04:50 PM
I'd never put much thought into it before, but where in history did our SO CALLED standard caliber sizes come from? Is there some formula that helps engineers come up with new calibers or do they just have a big "Magic 8 Ball" that tells them to come up with a new size? .303, .308, .223, .357, etc. For example the .308 (7.62x51mm) and the soviet 7.62x39mm ( which is actually a .310 ).
Is the .308 the result of testing that showed that the .308" diameter bullet performed better that the .306, .307, .309, and .310 sizes?
I know its trivia, but ther must be some sort of answer. Sort of like the way that the width of modern rail road tracks have origins based on the width of a Roman battle chariot.
[This message has been edited by chucko (edited June 06, 1999).]
June 6, 1999, 07:58 PM
I don't know about any particular system. I do know that in my testing, it took a lot of ammo, and lot of error to create a marriage of ammo and gun. Varing bullet weight, diameter, length and type, barrel length and finally pressure points on the barrel to stabilize during sustained fire, and powder etc. to achieve the best results.
These tests were conducted for the specific use of the firearm. Paper, distance, penetration and accuracy.
[This message has been edited by Harley Nolden (edited June 06, 1999).]
June 7, 1999, 02:09 PM
Of course, Guage (also called "bore") was the old number of round balls to make a pound formula.
Inconsistencies between the ".30-caliber" .30-06 and the ".308," using the exact-same dimensions, came from first using the pre-rifled bore diameter, then switching to designate the groove/proper bullet diameter.
I suppose the 7mms were a metric-based handy way to get decent long-range performance while using less materials than the 8mms.
Otherwise, I'm probably more clueless than most as to why it's generally a sequence of .22, 6mm, 6.5mm, .25, 7mm, .30/.308, .338, .35, .36 (well, 9mm/".38"/.357), .41, .44, .45 & .458 for most calibers.
10mm/.40 could be said to be the result of experimentation with .41 and switching to a handy round number.
June 7, 1999, 08:05 PM
It sounds rather incredible today, but most calibers "just grew." Example: S&W copied the French Flobert .22, then made a .32 when more power was wanted. Meantime, Colt made a .31 caliber percussion revolver and when some were converted to cartridge, it was .32. But they weren't the same .32; competition not permit that. So there is a .32 Colt, and a .32 S&W and they are not the same. Each of these anomalies has a long story. It is fascinating, and would take a book to describe all the ammo names and where they came from.
June 7, 1999, 10:33 PM
Guys rememberr that when it all started projectiles mooved kinda slow and needed to be rather large to have any effect. As blackpowder improved and velocities increased bullet diameter was able to decrease.
In the Revolution muskets ran in the large 60's and 70's in caliber. When the 45-70 was adopted by the US ARMY after the Civil War the main concern was it's SMALL BORE size.
I think that the calibers "just grew" as was stated in another posting. Manufactures and "Wildcat" developers were able to keep decreasing bore size as the weapons became more efficient.
As far as MM vs caliber. English and Americans "used" to think in terms of the inch (100 calibers to the inch) European think in MM (roughly 4 calibers to the mm)
June 8, 1999, 05:37 PM
The main source of confusion is due to the absolute lack of consistency. Jim Keenan touched on one aspect of it. Any proprietor who dreams up a cartridge can pretty much decide how he's gonna measure and name a bore diameter.
Some inch-measurement bores were measured across the lands; others across the grooves. This gives, occasionally, two different bullet-measurements which are really the same.
Another problem comes from conversions in numbering systems. One millimeter is 0.03937 inches. Folks have a notion that even numbers are better than Omigod fractions, so we have 10mm = 40-caliber...Which of course beats saying, "I have a 39.37-caliber pistol...
Yeah, the original shotgun gauges were numbered according to how many round lead balls in that size it took to weigh a pound. And then somebody came up with the .410 which ain't a gauge, but a caliber--and it interchanges with a .45ACP?
Cartridges in the 1800s gave a bunch of information in their naming. A .30-30 was a 30-caliber with 30 grains of black powder. A .45-70-500 was 45-caliber, 70 grains of black powder, with a 500-grain bullet. We all of course know that there are 7,000 grains to the pound.
I ain't gonna touch drams and dram-equivalents...
Again, an old book by Philip Sharpe, "Complete Guide To Handloading" is one of the better all-around sources of info on this sort of stuff. Some libraries might have it, or maybe used-book stores...
Hope this helps, Art
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