In the manual to my S&W .357 it says you may also use .38 and .38+P. I bought some .38+P 158 grain Black Hills ammo, but before I use it, I just wanted to confirm its definitely OK. Thanks.
The .38 spl in +P or non +P form is perfectly safe in any .357 magnum revolver. The .357 magnum cartridge is the most powerful of the 3 so the the 2 weaker cartridges won't harm anything. Truth be told more .38 spl cartridges are fired in .357 magnum revolvers than the .357 magnum cartridges.
There is no problem in using +p, actually it kind of nice using the .38's when target shooting with the 357 its a little cheaper , but remember you cant use 357 rnd in a 38 pistol , so have fun an fire away
Frequently, shooting .38 Special standard or +P in a .357 Magnum revolver may leave a small deposit ring in the chambers of the cylinder, but nothing that a thorough cleaning won't cure.