Well, the above are my two earliest J Frames, and here are some of my newest...these are the so called "Magnum J Frames", and are all chambered for the .357 Magnum cartridge.
From Top to Bottom:
Model 340 PD, .357 Magnum, shipped October 2nd, 2014;
Model M&P 340, .357 Magnum, Shipped October 29th, 2011
Model 640-1 Pro Series, .357 Magnum,
Model 640-1 .357 Magnum, shipped July 1999
All are No Lock variations. Of my three dozen Smith and Wessons, none have an internal lock, although I have reluctantly come to terms with the MIM parts. For the last few years, the 340 PD has been my most carried handgun. It's 11. Something ounce weight make it an extremely lightweight burden to bear!!
Best Regards, Les