Re: spotting scope for .30 cal @ 4 to 500 yds
Do you actually have that combination, or have looked thru it a number of times? I notice you are from across the pond, so perhaps the Optolyths aren't quite as spendy for you as they are over here; that rig you mentioned checks in at a little over $2k stateside. A good Kowa or Leica 80mm spotting scope w/ the fluorite lenses is a considerably chunk less and I'm imagining works pretty well (I know they can see .22 cal bullet holes in the black, if mirage and light arent totally hosed) for most uses.
If its not for competition, but for practice, a solution that often times works pretty well is to go get the 12" Shoot-N-C bulls, and put them up out there. Tends to show the holes pretty well. The bulls are a little spendy, at about a buck a pop, but you can get a pack of the 3/4" pasters for it and if you mount the bull on a piece of plywood or cardboard and take it home w/ you out of the weather each bull tends to last a loooong time that way.
As the saying goes, more than one way to skin a cat!