Dave, I bought a 640 back in 1995. I wanted the enclosed hammer as I would just drop it in my back pocket. Didn't want anything to snag on the way out.
I shoot only .357 in mine. It is a steel handgun and will handle the magnum loads just fine. It leaves a beautiful orange basketball at the muzzle. Don't let anyone stand beside you!!
I recently added Crimson Trace laser grips. It shoots where the red dot hits.....at the ranges I would use for self-defense.
Now days I carry it in an old Kramer holster that grips it tight. I can use it on the right side about 3:30 or on the left side at 10:30 for cross-draw while driving.