1. accurate declines, say from 1.5 inch groups at 25 meters, to 2.5 inches
2. the gun will need service and/or repair, and what these repairs might be
3. wear-out to the point of being unsafe, and what parts actually wear-out
easyrider: I expect what loads one shoots has a great deal of effect on longevity but I wore out a blackhawk in 357, here is what I noticed:
I was shooting 125 gr JHP with a full charge of H110.
I went to somewhere around 15,000 rounds before I sent it in for re-hab. Accuracy started to suffer after 10,000...The forcing cone showed lots of wear and it began spitting (powder, I think) for the last 1,000 or so.
The gunsmith said it need a new barrel, timing work, build up and re-harden some metal on the frame behind the cylinder (I think that is what I heard). If I had been shooting heavy hardcast at a more sedate velocity it would probably still be going. As it was, it took me 20 years to wear it out...I like the load, so I am going to keep shooting it...doubt I will get the rebuild worn out before my shooting days are over. FWIW, dvnv