The highest useful magnification for a good quality spotting scope with the typical 60 mm objective is about 45 to 48x. To get a high quality image at 60x would require a high quality scope with 80 mm objective combined with a very solid and stable tripod. Mirage, dust, haze, and poor contrast lighting will often present problems, and getting a clear image at 500 yards will probably require the best possible conditions. Even with everything at its best, you will rarely if ever be able to see a .30 cal bullet hole in the black.
Perhaps the best scope under the best conditions combined with a special target to make the holes more visible might work sometimes. For targets, consider some kind of reactive target or some special target which makes bullet holes more visible like Shoot-N-See.