For you to shoot with any accuracy at long range you have to have a round that launches a bullet fast enough to have the bullet still be supersonic at the target range (the bullet also has to have a good enough ballistic coefficient). The .308 and 22-250 won't come close to keeping a bullet supersonic at 1500 yds. The .308 takes a 30" barrel to get up enough velocity to keep a 155 gr bullet supersonic at 1000 yds, no way will it make 1500. When a bullet goes from supersonic to subsonic (roughly 1000-1100 fps) the pressure wave shifts around and accuracy goes to pot. That's why it takes big rounds shooting big streamlined bullets at fast velocities to shoot at these longer ranges.