If you are looking at an actual remington AR not just an AR in 260 for a 1000yd anything you are going to be disappointed. Actually any AR for a 1000yds is going to be a frustrating journey if your expectations are not realistic. By all means you can shoot an AR out to 1000yds but if you are expecting good enough accuracy to have a high probability of first round hits at 1000yds on a coyote you are going to be disappointed. You have to keep in mind that AR-10's are much more proprietary to their respective parts and manufacture also so when looking at aftermarket items, fit can be an issue. I would go with a DPMS LR260 as my base to build off of or if i wanted to just go with a factory rifle i would purchase a RRA. As far as velocity goes i have had very good luck in my LR260 with the 123 amax @2900fps. With the heavier 140's the most i could get without case head swipe was around 2700. An adjustable gas block would be a good investment before beginign load development with the AR.