I run a 260 with a 26" Criterion barrel. Topped with a 20 MOA Nightforce Base/Leupold Mark 4 Rings/Sightron SIII 8-32X56 LRMOA. Rifle is zeroed at 100. I have 62 MOA of elevation up with this combo. My 100 yard zero is obviously near the bottom of the scope internals. I've never had a problem with this setup and have used it on this rifle for 3 years and the same rifle in 308 for several years prior to that. I've shot inside 100 yards out to 1,792 yards (had to hold over with reticle for this after maxing out the scope). If you're looking to get to 1000 yards then get a 30mm tube. Remember if the scope has a total of 65 MOA travel etc that's only, playing it safe, about 30 MOA of elevation with a 0 MOA base. If you ever want to go further than get something like the Sightron 6-24 or something similar that has 100 MOA of total travel, matched with a 20 MOA base and you'll never have an issue. Don't bother looking at 1" tubed scopes for long range shooting.

I'd load the X-Caliber barrel with the longer bullets you want and roll with that before I'd hand ream your chamber out. The hornadys usually like about .020" jump. I'm running .010" off with 142 SMK. My bullets were still stable over a mile with the factory CBI reamer.

Just my $.02