Smith & Wesson has been making .45 ACP chambered revolvers since the
2nd MOdel Hand Ejector of 1908-1915 aka the "Triple Lock" was
changed for use by the U.S. Army. THe M1917 military designation was put on the N-frame S&Ws as well as the large frame Colt New Service had
the ball detent on the crane as well as the ejector rod removed for these
service pistols for the Doughboys in the trenches in WWI. THe rimless .45
ACP case was enabled for use in the revolver via the use of half-moon clips
which hold 3 rounds each, and enable the ejector star to gain purchase for
extraction. It was Horace Smith who invented the moon clip. The demand
for handguns for the troops was greater than the capacity to produce the 1911 Semi-auto pistol.
Post WWI, Cplt stopped making the large frame New Service revolvers but S&W continued production of the N-frames in .44 SPecial, .38 SPecial as
well as .45 ACP. WIth the surplus M1917s on the market or brought back
by servicemen Remington-Peters created the .45 Auto Rim(AR) cartridge
The .45 AR did not require use of moon clips since it has the same case dimensions as the .45 ACP case but it has a 0.0910 thick rim in order to
position/headspace the cartridge with the same amount of space moon clips occupy in relation to the firing pin.
Between the wars the N-frame .45 ACP sold on the civilian market but it
dwindled during the mid-1930s and S&W almost stopped
production of this calliber revolver. However, the Brazilian
goverment put in an order in 1937 for 37,000 - they are known
as "Brazilian Contract" guns identified by the Brazilian crest on the
Rear RH side of the frame. All of the Pre-WWII N-frame .45 ACP
S&Ws had fixed sights and a 5 1/2" Bbl. although with S&W there
might be the oddball special low production run.
Production stopped during WWII, it ramped back up in 1946 and
while the rest of the N-frames were built with the new shorter stroke
action the .45 ACP revolvers were still built on the PRe-WWII
longer stroke until they ran out of parts or whatever and in 1949
it was time for the .45 ACP revolvers to also get the shorter double
action design. Two models were built, the 1950 Target with
adjustable sights and a 6 1/3 inch Bbl. as well as the 1950 ARmy
a 4" Bbl. with fixed sights.
Bullseye shooters weren't satisfied with the 1950 Target so S&W
gave the design a no taper barrel with a 0.790 diameter - Target hammer
and Target trigger with the large Target grips this is known
as the 1955 Target. In 1957 when all S&W handguns were given a 2-digit
Model number the 1955 Target became the Model 25. MOst Model 25s
were built with a 6 1/2" Bbl. Len. through the 1970 but with S&W variants
exist.
In the mid-1970s, somebody came up with the Full moon clip which holds six cartridges. In the early 1980s, the Stainless Steel version, the 625 was introduced. Today, there also is the 325 xx variants with a Scandium frame and either a Titanium or Stainless STeel cylinder. Another current production variant(s) are the "Classic" line Model 22s, which have modern
internals and the front of the frame is sculpted to look like earlier N-frames
THe 22s resemble the fixed sights 1950 ARmy and the M1917.