I just bought one of the old police trade ins, a S&W #60 like a #10 but stainless. It came with the hammer bobbed so I called S&W and ordered a new hammer. My question is how difficult is it to take out the old one and relpace it with the new one? I've exchanged springs for Wolffs but not a hammer. Does it require fitting? I'd like to save $50 and do it myself.