The semi-plausible story about the S&W 45 caliber cartridge has been repeated so long and often by gun writers that it is accepted as fact by many otherwise knowledgeable people. The same lie told often enough.....
You scholars out there are referred to J.R. Mattern's book "Handloading Ammunition" published in 1926. He identifies the cartridge as .45 Colts (sic) and does even mention the shorter S&W version of the cartridge.
Philip B. Sharpe's book "Complete Guide to Handloading" published in 1937 describes the .45 Colt cartridge correctly and further describes the .45 S&W cartridge as "It is now an obsolete cartridge."
Herschel C. Logan's book "Cartridge" published in 1969 describes both the .45 Colt and .45 S&W cartridges correctly.
I have examined countless books and magazines (including every issue of "The American Rifleman" and have never found a reference to length of 45 caliber revolver cartridges prior to WWII.
My own speculation is the "Long" terminology originated after WWII by returning G.I.'s that had been exposed to Model 1911-A1 pistols and it's ammunition "Cartridge, Caliber 45, Model 1911" and felt they needed a means to differentiate between the auto pistol cartridge and the older revolver cartridge. No differentiation was needed then or now. The head stamp describes all one needs to know.
By the way, the U.S. military never chambered any of their firearms for either the .45 ACP or .45 Auto cartridges. Not the 1911 series of pistols, 1917 revolvers, Thompson Sub Machine Guns, M3 Greases Guns, Reising Sub Machine Guns or the Liberator Pistols. All were chambered for the Cartridge, Caliber 45, Model 1911.
In addition, the .45 ACP cartridge was obsoleted by the .45 Auto cartridge prior to WWII. Where have the gun writers been? Some people just never seem to get the word.
The .45 ACP, .45 Auto and .45 Model 1911 cartridges are not identical. Each is loaded and tested to entirely different Technical Data Packages using different pressure testing equipment, procedures and specifications for maximum pressure.
Just because two cartridges appear identical and might chamber in a gun with a different caliber designation does not make them identical and safely interchangeable. Pulse P cartridges are not the same and standard cartridges of the size. The .223 Rem cartridge is not the same as 5.56mm cartridges.
There is a formal process within the Sporting Arms and Ammunition Manufactures Institute (SAAMI) and American national Standards Institute (ANSI)to establish cartridge names. Laymen and ill educated gun writers and several rogue gun manufactures do not have the right to rename an existing cartridge or use obsoleted designations no matter how compelling their motives seem to be. It is no more appropriated to use obsolete cartridge designations than to address a married woman by her maiden name. Words have meanings.
Every SAAMI member and other responsible manufacturers have some form of the following warning on their ammunition packaging. "Use only in firearms in good condition marked and chambered for use of this cartridge"
Its the head stamp Stupid!