Everything that has been said I need not repete. I have a 638 for carry, if I feel I need a .357 I get out my Ruger SP101, all steel.
TBS, if I felt the need for close to .357mag out of my 638 .38 +p, I'd load it with +P short barrel buffalo bore 158g LSWCHPs. 1000fps
But I settle for GDHP 135g SB +Ps.