Howdy
Here is a photo that may help this discussion along. Left to right the cartridges in the photo are 45 Colt, 45 Schofield, 45 ACP, and 45 Auto Rim.
Cartridge revolvers had been around as early as 1857, but Smith & Wesson controlled the Rollin White patent for revolvers with chambers bored all the way through for cartridges. That is why almost all the revolvers used during the War Between the States (1861-1865) were Cap and Ball revolvers, even though cartridge technology existed at this time. S&W guarded their patent fiercely, and no American firearms company could get away with producing a cartridge revolver while the White Patent was still in effect. S&W would sue the pants off of them.
Around 1872 the White patent expired, and other firearm companies were free to produce cartridge revolvers. At this time, the US Army was looking to replace the thousands of obsolete C&B revolvers it owned. Colt won the contract from the Army, and by 1892 had sold 37,000 revolvers to the Government. These revolvers eventually became known as the Single Action Army.
The original caliber was 45 Colt. Period. The Cartridge Over All Length was 1.625, with a case length of 1.285. The bullet was a soft lead, hollow based 250 grain inside lubed bullet. These first cartridges were copper cased, not brass, and they used a now obsolete type of priming called Benet priming. Benet primed cases had a greater case capacity than anything else since, including balloon head cases. These were probably the only 45 Colt cartridges that could truly hold 40 grains of FFg Black Powder.
By 1875, Smith & Wesson had decided they did not want to be left out of the lucrative Army contracts. S&W was not producing any 45 caliber revolvers at this time, their large #3 Frame revolvers were all 44 caliber, either 44 S&W American or 44 Russian. And neither of these cartridges were as long as a 45 Colt, the 44 Russian cartridge was only about 1.245 long Overall. S&W asked the Army if a 44 caliber revolver would be acceptable, but the Army was adamant in wanting their new cartridge revolvers to be 45 Caliber. Opening up the caliber from 44 to 45 did not present a problem for S&W, there was plenty of meat in the cylinder and barrel to allow this. But the frames of the S&W #3 revolvers were too short to house a cylinder long enough to accept the 45 Colt cartridge. So Smith applied to the Army, and got permission to supply a 45 caliber revolver to trials with a shorter 45 caliber cartridge that would fit in the shorter cylinders. These new 45 Caliber Smiths were dubbed the Schofield model after the Cavalry officer who suggested a new latch design that allowed a mounted soldier to open the revolver with one hand. The cartridge Over All Length was 1.430, with a 230 grain soft lead, hollow based bullet. The powder capacity in the new round was about 28 grains of FFg Black Powder. All S&W large caliber revolvers at this time were top break revolvers, employing an extractor star to extract and eject the cartridges, so the new round had a significantly larger diameter rim than the Colt round, about .520 in diameter, to allow the extractor something to grab. Current 45 Colt rims are only .512 in diameter, but early 45 Colt rims were even smaller.
The Army purchased 3000 Schofield revolvers in 1875.
The Schofield revolvers did not remain in government arsenals for very long. Although no case has ever been authenticated of the longer 45 Colt rounds being issued to a unit having the 45 Schofield revolvers, it has often been theorized that Murphy allowed this to happen, and the 45 Colt ammo would have been useless to the units with the S&W revolvers. In any case, by 1880 the Army declared the Schofield revolvers surplus, and sold them off to civilian dealers. Many had their barrels shortened to five inches, and Wells Fargo bought up a lot of these shortened Schofields.
Yes, there were indeed some cartridges produced that were labeled 45
Long Colt, however they are unusual. Mostly, the cartridge has always been known as 45 Colt. Yes, the Army was known to call the cartridge 45
Long Colt when both 45 caliber cartridges were still in inventory. However, not many gun store clerks are aware of this history, and when you ask for a box of 45 Colt, they will usually ask you if you mean 45
Long Colt because they want to make sure you don't want a box of 45ACP.
P.S. Here is a photo of a couple of old cartridges from my cartridge collection. The cartridge on the left is a 44 Colt, the one on the right is an old UMC 45 Colt. Note the tiny rim, only about .505 in diameter. That tiny rim is typical of older 45 Colt cartridges, and is one reason why 45 Colt was never chambered in rifles until the modern era. An extractor hook could never have gotten a grip on that rim.
And here is a photo of some very early copper cased, Benet primed cartridges. The one on the left is a 45 Colt, the other one is a 45 Schofield.