I did a lot of 1000 yard shooting with the 308. I was having good luck with the 190 grain Sierra HPBT match bullet. Some of the bullets tend to go through the transition stage into sub sonic at about 850 yards to right at 1000 yards.
The 30-06 did slightly better due to the larger case capacity.
At 1000 a key hole was not that strange to find on the paper. I also had good luck with the 173 grain bullets as well. They carried there mass out about the same range. For powder a lot of us found that Thunderbird powder #2208 was about the best ticket out there for the 308. A lot of silhouette shooters used it as well I bought 250 lbs of it years ago, back in 80s I don't know if Eric has any left but he was in Laveen, AZ. I have had acceptable luck shooting BLC powder with the 190 bullet out of the 308. If you are shooting a m-14 or m1a I dont like to go much over 168 grain bullets. I found that the with auto loaders I limit my shooting to 800 yards
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This year will go down in history. For the first time, a civilized nation has full gun registration. Our streets will be safer, our police more efficient, and the world will follow our lead into the future!" -Adolf Hitler,1935"