I need to see 6.5mm bullet holes at 300m in the black. I can manage it most of the. The best I have come with so far is an Optolyth TBS 100 with the 20-60 zoom eye piece from a TBS 80 as this gives an effective 30-90 zoom on the TBS 100 (not sure why but I was told it does). Also there is a fixed 107x eye piece. I like this scope because it is good, tough and rubber armoured. As important as the scope is the tripod, Bogen/Manfotto are good (I like the heavy duty green job - 055 NAT3) otherwise in the slightest wind you get movement so however good the optic you ain`t going to see what you need.
That said a bit cheaper way and maybe a better way is to get astro type telescope (Meade) with a bigger objective and much more magnification, I know a few people who use them, they say they can see bullet holes at 500m no problem, but they are not normally waterproof and are a pain in the butt to set up, even on a concreate floor.
Even with good glass if the light is not right or the heat is bad I think it will be very hard to see what you want.
One thing you can try if your target is black, is to put a large piece of white material at about 4 to 6 metres behind your target. That way you can easly spot your shots, specialy with the sun in your back.
We use that technic at my shooting range at 300m. I have never tried further.
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!
I have the Optolyth TBS 100 with the 30-90x zoom and a couple of wide angle eye pieces. It is spendy but tough and good. The only other spotting scopes that I have to compare it with are an old Bushnell Spacemaster 15-45x which is now redundent as my Nightforce NXS 12-42 does the same thing (useable out to 200m to see bullet holes). I have seen bullet holes at 300m with the Nightforce but not often. Also I have a Meopta which is very good for the money. Living in CZ land it was fairly easy to get a boosted occular (109x) made but this gives you a very small exit pupil diameter.
Another thing which may be ok but I have only seen one is a Yukon offering it has a 100mm objective and I think you can switch between 6x and 100x.
One thing which people may have a different idea on is what is meant by "seeing a bullet hole". My idea is that I see the hole when I glance through the scope, I dont often have the time to look through the thing trying to find the shot for 30 seconds or so.
Here the police use Swarovski ST80`s and others use Leica`s or Zeiss or Meopta.