If it is for a course I am taking my Sako TRG in 308 win. It has a 27" barrel and will run 168 Amax or 178 SMKs to a grand with no problems. It will also help you hone your fundamentals and ammo is available just about anywhere. Mine likes Hornady or Federal GMM so well I don't even reload for it anymore. I hunt with Hornady Black 168 AMAXs, perfect whitetail medicine to 600 yards out of my 16" gun. You just about can't go wrong with a 308 win for anything inside a 1000 for course work. I have made a cold bore shot with my Sako at 1250 using 178 SMKs. The 6.5 Creedmoor works for the same reasons if I am running factory ammo.
My favorite hand loaded cartridge and rifle is a 6.5x284 Norma. It will do everything my 300 WM will do at half the recoil. It is good to a mile on steel. For anything beyond that and for hunting to a 1000 yards I have a custom 338 RUM AI with a long throat and a 27" barrel. I prefer it to the edge and the LM because it can be built on a Remington action and loaded in a Wyatt's box and you could possibly find factor ammo in a pinch if you had too, though my gun hates factory ammo.
I think if you stick with 308, 6.5 or 338 you will be fine. There are tons of factory and custom rifle options in these calibers and cartridges. 338 is probably a little overkill for most courses. I have never seen one that shot beyond a grand for the actual course. Think 308 win, 6.5 creed, 300 Win Mag in factory options. They will also give you the best barrel life. Nothing fancy just solid choices. A 300 win mag would also serve you well for elk size game to 800 yards, though recoil, cost and fatigue may become a factor on an extended day shooting course.