A lot of the discussion is interesting, but may not be helpful. I would recommend the questioner listen to the recent Hornady podcasts regarding actual, statistically proven, rifle accuracy, versus the accuracy we riflemen claim we have out of our rifles (episodes 50 and 52). The ultimate reloader podcast with Bryan Litz is similar, but less detailed. Getting a 0.5MOA best group in ideal conditions off the bench is possible when the precision of the rifle in fact is in fact significantly greater than that. But is that really the issue? And are you a shooter or a hunter? There are many folks who practice frequently, know their rifle, and are capable of very precise shooting at long distances. If they are hunting, they are also most likely carting around a lot of equipment, including an accurate Kestrel to aid their shooting capabilities.
A much more important question, assuming you have a rifle that is actually capable of shooting true MOA or better groups, is are you capable of shooting those types of groups in actual field conditions at the distance you have listed? I would say, and this is no afront to you, is that you will not be capable of reliably hitting an 8inch target at 800 yds in field conditions. Unless you have access to a shooting range for long distance shooting, will be practicing regularly, and expend hundreds of rounds practicing prone, sitting, shooting off trees, shooting on irregular ground, and regularly shooting in 15-20 mile an hour wind, you are not going to be able to consistently hit an animal, even a large animal like an elk at 800 yards. You can go to the Barbour Shooting School for a few days, shoot in an enclosed room, use a suppressed, smaller caliber rifle, get good instruction, shoot comfortably sitting off of a bench and hit a steel target at 800 yds. That is not western hunting. That would be like saying because I can comfortably drive a nice stable car down the interstate at 100 miles an hour in the open west, therefore I am ready for a Nascar slot.
Are you going to be able to hit an elk at 800 yds when you are lying on rocks in the snow, the wind, as it usually is, blowing 15 MPH or higher, and gusting, your hands are cold, there is a canyon between you and the elk? Do you know how much elapsed time it takes for the bullet to traverse the distance between you and your prey?
I live and ranch in New Mexico, and have shot lots of elk in my lifetime (70 years), here and other areas in the west. My children hunt, and between us we have lots of elk harvested. I have also guided elk hunters. I can't think of an elk we (family) have had to shoot over 300 yards. Could we have attempted shots greater than that distance? Yes. Did we need to shoot farther than that? No. I realize, that at times the hunt is winding down, you have a chance at a long shot, and it is either now or never. For most hunters, the answer should probably be never. I reload out of my garage, walk out to a bench 30 yards from my house, and can practice on targets, reload, and shoot some more. Or walk another 200 yards and begin shooting out to 600 yards or more. I love accurate and precise rifles, but extreme input rifles are not usually what makes for a succesful hunt. A few years ago my brother and I were hunting and got elk with him shooting a pre-64 Winchester lever action 308, and me a pre-64 bolt action Winchester 308 (built in 1953, 1 year after my birth). The shots were not from long range, but not in an easy situation to shoot from, and accomplished because we had acceptable hunting rifles, good hunting skills, and were capable of shooting in actual hunting conditions.
This has been too long, but I hope you can find a decent rifle, get familiar with it, and get an opportunity to come out west to hunt. There is not much more exciting than elk hunting. But I believe you would be a lot more productive if you would spend your time practicing shooting with a rifle you really know, and forget about trying to shoot at what is for most people an unrealistic, or even an unlikely distance. Good luck!
