I was talking with some friends about my firearms, and we were discussing the difference between modern US military cartridges (9mm and 5.56) and historical (.45ACP and .30-06). Looking at the four cartridges next to each other, it dawned on me that the pistol and rifle casing from each generation have nearly the same diameter. In order words, the diameter of a 5.56 cartridge is (or nearly is) the same as the 9mm, and the .45 seems to have the same diameter as the .30-06. Is this by design? Is the brass from a pistol cartridge just a trimmed down version of a rifle cartridge? Is this part of a war time manufacturing technique?
Obviously this isn’t a vital question, just a curious question that came up.
They are close, but not exact. The wall thickness of the .308 and 30.06 rifle cartridges are thicker than that of the .45acp and they are also tapered. The walls of the .45acp are straight and thin.
I have worked with a friend making .45 blanks from cut down 30.06 rifle cases and a star crimp. For blanks, they work fine....for loading bullets, the inside of the case would have to be reamed to accomodate a .451 diameter .45acp bullet.
In a pinch, YES you could make .45acp ammo from .308 and 30.06 rifle case....but have your micrometer and a reamer ready.
Looking at the dates of development of the various cartridges, 9mm luger 1902, the .223 in 1957 (as an experimental)
the .45acp in 1905, the 30.06 (a modified version of the original 1903 cartridge) adopted in 1906 as the standard military cartridge, I don't really see any connection between them as far as deliberate design.
There are many cartridges that use the same shell plate in reloading presses. This is because the differences in rim and groove diameter are minimal and fall within tolerances enough to not warrant making a different plate.
One thing the common(close enough for government work) base of the pistol and rifle cartridges provides for is rebarreling a rifle in a pistol caliber without having to modify the bolt. There is a company that sells a .45acp kit for the 8mm Mauser. By changing the barrel and inserting a new mag well, it uses standard 1911 magazines. No work is necessary on the bolt at all.