Re: spotting scope for 600 yrds
Magnification is important, but more important is the quality of the glass, and the atmospheric conditions. Bore size can be an important factor too.
I would encourage you to use some shoot-N-see targets as it will enlarge the area around the bullet hole.
I have a Leupold 12-40HD spotting scope, and I will be soon be using a Vortex HD Razor, with both eye-pieces.
Most of the time when I am practicing at distance I shoot at steel painted white, and in good conditions I can see hits beyond 1200 yards with my rifle scope.
The only time I have every seen bullet holes in a paper target at 1000 yards, was at Missoula, during the sighter period. I saw three bullets holes, then the conditions changed and I couldn't see them anymore. Bore was 6.5 and the scope was a S&B PM2 5-25 with ART Reticle.