The Colt 357 was made from 1954 to 1961, with a total production of around 15,000 guns.
It was available in blue or bright nickel, 4" or 6" barrel, and choice of either target stocks and hammer, or smaller "Service" grips and hammer.
The 357 was a VERY innovative gun.
It was the world's first mid-frame .357 Magnum revolver. Before this all .357's were large frame models like the Colt New Service, or S&W's "N" frame.
The 357 was the first modern center-fire revolver to use a frame-mounted firing pin, and the first to use Colt's now-famous target grips and hammer.
The 357 was intended to be Colt's premium holster revolver, and for people and police departments on a budget, the "budget" Colt Trooper in .38 Special and .22LR were offered.
In 1955 Colt introduced the "Super Premium" Colt Python, and things got complicated at Colt.
The only real difference between the 357 and the Trooper, was the Trooper has a lesser quality finish, and a firing pin mounted on the hammer, instead of in the frame.
The difference between the 357 and the Python was the Python's much better finish, and the heavy, lugged and vent rib barrel.
As it happened, people and police departments wanting a good, adjustable sight holster revolver bought the Trooper, and people wanting the best, bought the Python.
This left the 357 as "odd man out", so in 1961 Colt discontinued the 357.
At this time, Colt added the .357 Magnum caliber to the Trooper line, the hammer-mounted firing pin was discontinued, and the pin was moved to the Trooper frame.
From then until the Trooper was discontinued in 1969, it was available in .357 Mag, .38 Special, and 22LR.
Since the 357 and the Python are the same gun other than for cosmetics and more hand fitting of the action, the 357 is viewed as a "poor man's Python".
These are extremely high-quality pistols, and a bit of a "sleeper" as most people have never heard of the 357 model, and pass over them, mistaking them for the look-alike Trooper.