A number of manufacturers used the designation "model 4". If you can give us some information, including make, description, markings, we may be able to answer your question. It would also help to ask a question- which you have not done yet. What do you want to know?
It should be marked as to caliber on the barrel.
Can't be answered without knowing ALL markings, type of action and who made it. The caliber will be marked on it somewhere. Might be worn off.
The Model 57/657
Unable to identify model from just the serial number. Need a detailed description of all markings, type of action, finish, caliber.
model 1900 fitchburg mass usa A38473
Which model, what condition, condition, and condition?????
S&W Model 16, Colt
They refer to this handgun as the browning model BDA (browning double action auto) pistol.
It depends on the make and model. Is it a double action or single action revolver?
Colt Model 1877 "Lightning" Double Action Revolver in caliber .38 Colt and the similar revolver model "Thunderer" in caliber .41 Colt.
100 or so
100-1000 USD