I have a 6.5 X 284, but I only use it for matches, but it slings the heck out 140 Bergers at 1,000 yards. The Elk rile is a 264 Mag. using 160 Matrix being pushed out the tube at 2900 f.p.s. The Deer / Pronghorn set up is a 6.5 X 55 throwing 140 Partitions at 2650 f.p.s. I have never tried to take game at 800 - 1,000 yards, my longest shot to-date is a little over 200 yards. Hope your build turns out well, post a few photos when you are done. I finished my 338 Mag. build while in quarantine and I hope I get to use it this fall.