Re: .340 weatherby magnum
To 800 meters it will do anything the others will. From all my testing there is an average of about 125 fps between it and the RUM's with the lapua edging it by 150 fps or so. Not enough to make any difference to 800 yards. If you can get the 340 easily and the others would be way more expensive probably not worth the extra cost. You can buy remington 300 wby brass and neck them up easily for cheap brass. If all things are equal price the 338 RUM would be the best choice. The 340 wby was my second long range rifle back in the 70's that replaced my 7mm-300 wby. I took several animals beyond 1000 yards with it with the 250 sgk because in those days that is all we had. Now with better bullet choices the 340 wby is better and a very good 800 meter rifle and beyond.
Predictions are difficult, especially when they involve the future