It should be marked as to caliber on the barrel.
The Model 57/657
Which model, what condition, condition, and condition?????
S&W Model 16, Colt
Ask a gunsmith for help
100 or so
50 or so
5-50 or so
100-1000 USD
The model 19 is a 9mm only proposition. The model 19 is not available in .40 caliber, but the model 23 is the same size gun and it is a .40 caliber gun. Some people would say that the model 23 is the .40 caliber version of the model 19.
Model numbers were not used before @ 1957.
Impossible to say without a more detailed description of the handgun in question.