I've had--and carried--a 642; my typical carry gun is an M&P340. Over the years I've carried anything from 'FBI-800' loads--(38+P, 158-gr. by various mfrs) on up to the Buffalo Bore 20A--their 'Heavy 38+P' 158-gr. round. The 20A is more than I care to tolerate even when my hand is in good shape--but this 20D should be a fine round for a 442 for SD use, IMO. It about replicates the original FBI load, with a different bullet--arguably, a more effective one.
The issue really becomes practice and conditioning--you can shoot anything if you are tough enough, but to get tough enough, you have to practice--a lot.
Learn to reload, if you don't already do it, and then sort out building a 'replica reload' of your carry ammo. In this case, 158-gr. LSWC powered by AA#5 or Ramshot True Blue will do about 860 fps from a 2" barrel, when loaded to 38-CIP standards. Those rounds will cost you perhaps 13 cents each to build and allows you the practice you want to do.
Will rounds like this wear out a 642? yes. But all shooting wears a gun out. If you're the original owner of a 642, S&W will stand behind it.
Jim H.