For the range that you specify on Elk, I think that a magnum would be the choice, which would be a better fit for a long action, particularly if a magazine is to be used. Since you did not allow for two bolts, and a magnum bolt face would not be suitable for a varmint cartridge, and for that job, you could single load, I suggest an action that has interchangeable bolt heads. There are a couple that I can think of. On the less expensive side, a Savage could do the job. For a larger budget, something like a Bighorn would be a suitable candidate. Being able to have different bolt heads will allow you pretty much anything that you want for calibers. The Bighorn actions are Remington clones that have built in recoil lugs, in the same position that they would be if they were a separate piece. They take Remington pattern triggers, so you can have a Jewell if that is what you want. There are lots of suitable stocks. For the volume of shooting that prairie dog shooting entails, you do not want to go with too large of a case, unless you want to spend a lot of time waiting for your barrel to cool, and barrel life is not a consideration. A fast twist 6BR should have the reach with longer bullets, and it should shoot lighter bullets as well. For elk, at the distance that you specify, to have the most confidence, something like a .338 Lapua with a muzzle brake would be the ticket. If you shorten the distance requirement something smaller would work just fine, but I think that for really long work, you need to start out with enough energy so that you will have enough when you get there. I have a friend who has hunted elk on a large private ranch for many years. He plans on long shots, and has used several rifles in different calibers. His latest rifle project was in . 338 Lapua, and it has done and excellent job for 600 yard shots. I do not like to see shooters use calibers that deliver marginal energy at long ranges for animals such as elk.
