What ammo should be used for a smith and Wesson model 10 38 revolver?

In MOST cases, the Model 10 is a .38 Special caliber. The barrel should be marked to show this. .38 Special (sometimes written as its original name- .38 S&W Special) is a different cartridge than .38 S&W. Early Model 10s may not but suited for frequent use of +P rated ammunition- it is loaded to higher power levels. The traditional cartridge was a round nosed 158 grain lead bullet- but 125 grain jacketed hollowpoint is frequently used for defense, and 144 grain wadcutter is used for target shooting.