YOU DON'T HAVE TO HAVE A CUSTOM RIFLE TO SHOOT ACCURATELY TO 600+ YARDS!!!
I was looking to do the same thing 2 years ago. I finally decided on a stock savage 112BVSS in 7mm rem mag. I had the action bedded and the muzzle re crowned. That is all. I then topped it with a Leupold VX-II 6-18 target scope with the target turrets. I mounted the scope with burris sig rings with the offset inserts to get me the elevation I need to get to 1300 yards. On a leupold one piece base. And not to forget a Harris Bi pod A must for hunting long range.
Now this combo is certainly "unique" looking. It shoots increadibly well. You didn't say wether or not you reload? But my rifle can shoot a 3/8" 5 shot group at 100 yards. I was shooting the other day at 551 and ended up with a 4" 5 shot group. Then was shooting later and shot at 862 and made a 5 shot 8.5 inch group. Then stretched it out to 958 and made an 11.25 inch group.
The gun seems to be sub MOA out to 850 or so. And a 6 inch group at 600 yards will kill deer no sweat!
The only down side to this combo for you is that it's about 14-15 pounds total weight, which is slightly over what you want.