I just picked up a gently used, no lock 640-1 (I already have a no lock 642 which I love). Question though...it's a 640-1, ser.#CET5xxx, in original case, and the spent sample in the case says it was test fired in may of 2001. The marking on mine are slightly different than in the photo's on this forum. The left side of the barrel has no markings at all, and the right side of the barrel say Smith & Wesson, with 357 Magnum just below it. Is this unusual? When did S&W change over to the locked version? Thanks to all...