go to the Ohio 1000 Yard BR club site and read the match reports on the Mile shoots (actually 1680 yds). I think best group is about 12" for Ohio and guy shot a 10" in Iowa a year ago with Savage 7 WSM he built up himself.
I shot a 5 shot 18" group with a 300 WSM shooting 210 JLKs.
Most are big 30 cals, or 338s and few 408s. My regular real LR rig is Rampro action, 34"lilja barrel in 9" bedding block with Unertl BV20 scope. Chamber is 338 Lapua Ack Improved. Pushes 300 gr bullet right at 3000 fps.