Scope
You will need a very good quality scope with at least a 60 mm objective lens to see small holes at any thing over 100 mt, and its more about the quality of the optics than the magnification.
Don't know where you shoot, but at Bisley there are electronic targets, or the TR ones with markers will have an orange disc which are easily seen with most scopes.
We shoot ISSF 300 mt at Bisley with the 300 Metre Target Club, and we have all electronic targets, the only time we use a scope is for wind mirage reading.
Have Fun
Robin
Walther KK500 Alutec expert special - Barnard .223 "wilde" in a Walther KK500 Alutec stock, mmm...tasty!! - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?