When I took that Coues at 517 yards, my 308 had a 3-9x40TV Tasco World Class from the early 90's. Actually that scope is still on it.
What I figure is the Vortex, Zeiss, and Minox scopes have better glass and overall are better than my old trusty Tasco. That being said, I would have no issue at 600 yards if my Tasco still had plenty of distance left to be max'd out. I might hesitate beyond 600 but I haven't used the newer scopes yet to say for sure.
The experience you guys share is greatly appreciated.
Kique
