If your going to shoot numerous rounds I would back off the 300 WinMag. Look for a soft recoil round such as the 6.5 Grendel, 6.5x47 Laupa, or 6.5 Creedmoor. Other rounds that completers use at 1000 are the 243 Win and 6mm Creedmoor. Hell the new 224 Valkyrie with heavy .224 match bullets is accurate to 1300.
Yep, it may have been Legion when those pictures were taken. There was just the top deck on the Conex boxes then. They have lengthened the line to the right, from this view, maybe changed the deck some up top and have opened up the center Conex box to shoot from benches through windows. At times there have been so many of us there we had to shoot from just in front of the chasm about 200+ yards ahead of this...you can see it in the picture.