Most factory rifles can be tuned to produce the necessary amount of accuracy for shots in the 400 yd range, but the 600 yd range is another story. Encores CAN produce top-notch accuracy. I'd go with a custom heavy barrel from MGM if you want to use the Encore, vs a factory barrel. I would also get another frame, and leave the barrel on it, I wouldn't switch back and forth. Get a trigger job that takes it down to the 2lb range too. That would take one more variable out of the picture. I would demand that the rifle I use for shots like that to produce .5 MOA at 100 yds, but I would shoot it out to 600 yds to see how it groups at that range (if you want to shoot that long). It would have to shoot less than 6" at 600 yds for me to take a shot like that. If you don't reload, you'll have to start, more than likely. All the shooters I know and read about that shoot at long range reload their own, and they weigh cases, bullets, etc, to get the most consistency that they can. Once you go past 400 yds, there are so many variables that come into play......the biggest being YOU. If you can't/won't spend the time and money to practice shooting at that range (from field positions, not a bench) with a 7 Mag, then don't hunt at that range with it.
Yeah, you can practice at long range with a varmint gun, but that doesn't replace shooting the actual gun you plan on hunting with. Also, if you are hunting out of a treestand, forget shooting 600 yds. With the exception of what was basically a tree house built in a huge old oak tree (it was about 5 feet thick at the base), I've never been is a stand that provided enough stability to shoot that long whether it was a permanent stand, ladder stand, etc.
