I have an older 77 mm Kowa with the Flourite crystal lense.
Admitted,I'm at 5000 ft altitude. I'm not talking in a black bull,but with orange and white sight in targets,I can reliably see .223 bullet holes at 300 yds.
Every time I checksights on my 257,its zeroed at 300 yds.I have no problem doing it from the bench.I only go downrange to pickup the target.
I won't say I can typically do this,but one ideal day,I could see .30 cal holes in a black bullseye at a lasered 500 yds.
Mine has the 20-60 zoom. Depending on light,I don't gain anything above 40 or 45 X.
I suspect a fixed eyepiece might be a bit superior.I wear glasses,I think I'd like the LER lense about 32X.
I'd recommend Kowa.I think the Flourite lense helps.
FWIW, I bought an old NRA model Bauch and Lomb.Its maybe 60 mm? or 50mm. Fixed 20X.Made in the 30's.It resembles the Military version,but a little smaller.
Once again,not in a black bull,but with orange and white targets,it sees .22 bullet holes at 200 yds,no problem.
Neat feature,you turn the eyepiece to focus,but there is a "rapid" function where you pull /push the eyepiece through clicks for a coarse adj.
When I get target focus,one click pulling back gives a beautiful mirage focus.