I have seen the .223 do well at 1000 yards just punching holes. Unless you are VERY versed, you will not do it. They do not shoot .223 because it is superior, but because of internal rules and politics within the military. There are many preparations of the rifle AND the ammo. Don't forget, the AMU and Marines have a big budget and lots of technology and time to work with things you do not have. They can choose to overstress a gun and scrap it after every match if they want. (I do not know that they do that, but they can) I have actually shot 7.62 service rifle at 1000 yards. Even with an M-14 you have your hands full and special prep is required, even with 175 gr ammo. I spent a long hot frustrating day in the target pits pulling for guys that thought they could shoot an AR at 1000 yards. Few bullets actually hit the target, and trying to find little pin holes in 36 square freet of target paper is annoying. Not the perfect rifle for long distance if you can avoid it.
I have also made 60 rounds for record plus sighters shouldering a 300 win Mag. That is a pretty abusive cartridge for the shooter, but the 190 gr bullets carry a lot of energy to the target accurately.
I have also made 60 rounds for record plus sighters shouldering a 300 win Mag. That is a pretty abusive cartridge for the shooter, but the 190 gr bullets carry a lot of energy to the target accurately.