S&W steel J and K frame 38's stamped with a model number are safe for 38 Special +P, that's per Smith & Wesson. I would think they would know when it comes to such things. Will +P blow up a 38 Special that is in good condition? No. Will it accelerate wear? Yes, and with older revolvers that used a "softer" steel or lacked heat treatment, the accelerated wear will happen faster.