Originally Posted by Steve C

The S&W model 39 is a 9mm semi automatic pistol. Assuming you are asking about a model 30 Regulation Police chambered in .32 S&W Long you should NOT USE any modern magnum ammo. Such ammo should not fit in your pistol and if it did the pressures are much higher than that for the .32 S&W Long which could result in damage to the gun or shooter.

You should use .32 S&W Long or .32 Colt New Police (NP) which is the same thing but would be a very old box of ammo. You can also safely shoot the .32 S&W which is a earlier lower pressure and shorter revolver cartridge of the same diameter that the "Long" was developed from.

A .32 ACP round designed for semi auto's will also chamber and fire in most .32 S&W revolvers but should be used only as a poor last alternative. The .32 acp was not designed for revolvers and with their higher pressure could be an issue if used in old top break revolvers but should not cause any damage in a later built model 30.