So, pick up a book, perhaps one on reloading, the technical info is all there. Hint 9mm, .38, and .357 =same bullet diameter for all three and, no, a 44 caliber is not exactly .44 inch. I learned all this and more from books, Bookwriter!
There's a slight variance between 9mm and .38, about .002". The 9mm is .355" in OD (that's outside diameter) and .38 is actually .357" in OD. Those are what's known as "nominal" sizes, as in "Plus or minus .001". The .357 Magnum is the same case as the .38 special, but it's .100" longer, and it's loaded to about twice as much chamber pressure, so it delivers about twice as much striking force.
The .44 mag is .429" in OD. The older revolver cases were loaded with black powder, ya see, as in the .44 Russian, the .38 Long Colt, the .41 Long Colt, 44-40. Their bullets had a reduced diameter "heel", like a .22 lr has. In other words, the bullet's OD was the same size as the OD of the brass cartridge case. The bullet's lubricant was on the outside of the bullet, and it was greasy. It picked up debris, and then sometimes couldn't be inserted into the chambers of the revolver. So the decision was made to make the entire bullet of an OD that would fit down inside the case. This meant that bullets either had to become smaller in OD, or the barrels, cylinders and frames had to be enlarged. It was much simpler to make the bullets smaller than to enlarge everything else. So the .32 came out to be .308", the .41 was actually .387", and so on. Cartridge "nomenclature" (ie, naming) is pretty arhaic and non-sensical in many ways.
BRASS, you ain't drinkin gasoline again are ya? I know that dream about Rosie and the machine gun really bothered you but, GET A GRIP MAN! :roflmao1:
Bookwriter: getting into calibers versus actual dimensions is opening a can of worms. Andy relayed some of this. But how about: .30'06 (thirty caliber of 1906) is really a .308 bullet. The .303 is really .311. The 7.62x54R, while supposedly the same diamter as the 7.62x51mm (.308) it's really .3105. The .45 ACP is really .452, so is the .45 Colt, unless you're talking the .45 Colt originally produced for the original Peacemakers, which is .454.