BrianM: I don't know why a S&W rep would say something like that. All newer S&W 44 magnums, especially the 629s, were upgraded to shoot heavy loads about 10 years or so ago. The only problem they had with the heavy loads was for folks who shot 300+ gn slugs over heavy charges on a regular basis and sometimes the heavy recoil would allow the cylinders would come unlocked. That problem was fixed.
Also, please understand that most factory literature, and reps, do not advocate the use of reloads as they cannot control the quality or safety of those loads and that constitutes a liability for them.
My older M29 uses 295-300 gn swcs. That is all I shoot in them. My revolver is fine, it is my wrist that takes the beating. You will not have any problem with heavy reloads if you reload safely. You can also purchase some very heavy hitters for those revolvers and they are safe in your 629. HTH. Mikey.