Art Eatman
Staff in Memoriam
"...the relationship between caliber and cartridge is one of those things that I kind of, sort of, understand, but really don't. Especially when the discussion turns to wildcats, but also with some of the more common rounds, including those that are actually over- or under-sized compared to their standard designation. Would you mind providing a little refresher course? Thanks!"
Caliber, of course, is merely the term for diameter in hundredths of an inch. So, a "twenty-two" or a "22-caliber" has a diameter of 0.22 inch. The variations in cartridge case shape and size came about from various individual minds as to the desired performance.
The actual names and designations of cartridges has no consistency in most U.S. stuff. Many European cartridges are IDed by diameter and case length (in mm) and with an "R" if rimmed. In the black-powder days in the U.S., the charge weight would be part of the designation, as in .45-70.
I'm not sure, but I think nowadays that most rifle barrel and bullet designations are for the diameter of the bore. That is, the groove-diameter, not the diameter measured to the lands. The grooves are approximately 0.002" deep, which is the same thing as saying the lands are 0.002" high. This varies among barrel makers. Somebody who's actually bothered to measure may jump in, here.
I know at one time you could buy .22 bullets for reloading in .223, .224, and on to .228. (Loading a .228 bullet into a .224-barrelled Swift made for a bit of excitement.) The old standard for 30-caliber was a bullet of 0.3085-inch diameter, FWIW.
"Wildcats": Hark back to muscle-car days, and think, "Street Rods". Or go to a custom-car show. Same deal. You can go from scratch and develop a cartridge, or you can take a showroom-stock dealer's product and modify it--and then put your name on it or some name you've dreamed up. If a factory adopts it, it's no longer a wildcat.
For instance, the .22 Hornet came out as a factory cartridge, IIRC; Lyle Kilbourne reamed it out and it became the K-Hornet. In the 1930s, several people meddled around with the .250-3000 Savage, necking it down to .22 for prairie dog shooting. Jerry Gebby's .22-250 "Varminter" became popular, and then Remington adopted it.
"Overbore": Some cartridges, in order to get high velocity from heavier bullets, have very long (comparatively) cases. The 7mm Rem Mag is an obvious example. To get the most efficient combustion, slower-burning powders and longer barrels are required. In non-magnum category, the .30-'06 has this characteristic. It works best with a 26" barrel and powders such as IMR 4064.
Somewhere along the way, it was learned that a somewhat shorter case would yield 90% of the velocity with some 80% of the powder--which is where the .308 is. And, it can do this with some four inches less barrel length. Another benefit is a shorter action--which is a bit stiffer as well as a bit lighter. Stiffer means a hair better accuracy. The next evolutionary step is this new series of "Short Magnum" cartridges.
So there's a bit of an overview. There are pages more of details, of course...
Art
Caliber, of course, is merely the term for diameter in hundredths of an inch. So, a "twenty-two" or a "22-caliber" has a diameter of 0.22 inch. The variations in cartridge case shape and size came about from various individual minds as to the desired performance.
The actual names and designations of cartridges has no consistency in most U.S. stuff. Many European cartridges are IDed by diameter and case length (in mm) and with an "R" if rimmed. In the black-powder days in the U.S., the charge weight would be part of the designation, as in .45-70.
I'm not sure, but I think nowadays that most rifle barrel and bullet designations are for the diameter of the bore. That is, the groove-diameter, not the diameter measured to the lands. The grooves are approximately 0.002" deep, which is the same thing as saying the lands are 0.002" high. This varies among barrel makers. Somebody who's actually bothered to measure may jump in, here.
I know at one time you could buy .22 bullets for reloading in .223, .224, and on to .228. (Loading a .228 bullet into a .224-barrelled Swift made for a bit of excitement.) The old standard for 30-caliber was a bullet of 0.3085-inch diameter, FWIW.
"Wildcats": Hark back to muscle-car days, and think, "Street Rods". Or go to a custom-car show. Same deal. You can go from scratch and develop a cartridge, or you can take a showroom-stock dealer's product and modify it--and then put your name on it or some name you've dreamed up. If a factory adopts it, it's no longer a wildcat.
For instance, the .22 Hornet came out as a factory cartridge, IIRC; Lyle Kilbourne reamed it out and it became the K-Hornet. In the 1930s, several people meddled around with the .250-3000 Savage, necking it down to .22 for prairie dog shooting. Jerry Gebby's .22-250 "Varminter" became popular, and then Remington adopted it.
"Overbore": Some cartridges, in order to get high velocity from heavier bullets, have very long (comparatively) cases. The 7mm Rem Mag is an obvious example. To get the most efficient combustion, slower-burning powders and longer barrels are required. In non-magnum category, the .30-'06 has this characteristic. It works best with a 26" barrel and powders such as IMR 4064.
Somewhere along the way, it was learned that a somewhat shorter case would yield 90% of the velocity with some 80% of the powder--which is where the .308 is. And, it can do this with some four inches less barrel length. Another benefit is a shorter action--which is a bit stiffer as well as a bit lighter. Stiffer means a hair better accuracy. The next evolutionary step is this new series of "Short Magnum" cartridges.
So there's a bit of an overview. There are pages more of details, of course...
Art