Early Model 29s had issues with repeated doses of the full power of the .44 magnum round and it took several revisions to get it right. As I recall this occurred around the 29-5 and the 629-3. My 629-4 Classic DX (below) is simply an awesomely accurate and fun to shoot revolver and I would recommend it to anyone who loves to shoot fine revolvers in a heartbeat.
Here are some articles you may find interesting in your quest:
http://www.sixguns.com/BookOfThe44/bot44c21.htm
http://www.sixguns.com/range/SmithWesson44Mag.htm