Firing it in single action or double action mode shouldn't make a difference. You stated it was "PMC ammo", you could be right , I've seen some imported ammo that isn't worth buying. If you have friend that has a S&W 'K' or 'L' frame revolver you could compare the two as to how hard (or easy) it is to cock the hammer. Check that main spring strain screw (under the grips on the front of the grip frame) and make sure it is screwed all the way in, then try some different ammo IF you can find any. .357 and .38 Special are still hard to find. If S&W wants you to send it back to them, check with the dealer you bought it from, chances are he can ship it for less dollars than you can and as good customer service he should help you with this.
