The M29 & 629 received a "Durability package" upgrade around 1990, to help them withstand a steady diet of heavy bullet loads, which were becoming more & more popular in those days. IIRC it was additional heat treatment of components.
Yes, the .45 Colt naturally does have thinner cylinder walls and barrel shank, which leaves less safety margin. I wouldn't try .44 mag loads in one.
The other point is, a DA revolver would be chosen over a single action for rate of fire, at extreme close range. Whether it is a two legged or 4 legged assailant, a 250-270gr load at 1000fps is going to have less recoil than a 300gr at 1300fps, and be easier to fire accurately, in a dire situation.
I like my 5" M629, and have carried it in bear and mt lion country. For big bears, my .480 Ruger would get the nod.
One of these days I need to get me a M25-7. Always have liked 5" S&W's
