A friend who is a High Master X-course shooter built a 284/M14 about 20 years back. He made a LOT of mods to it, but it did as well as any bolt gun at the tme. That being said, The 284 can achieve a LOT of pressure. An gas gun can't take that kind of pressure, so you need to load it down to around 7mm-08 velocities. so you may as well go with a 7-08 f you want a 7mm.
I spoke with that outfit a while back. Frankly they were kind of curt and said they arent taking on any new AR work at this time. I was inquiring about their 450 Marlin offering.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">ATTENTION: SALE ON ARMALITE AR10 308 20 ROUND MAGAZINES VERY LIMITED QUANTITY $79.95EA. DUE TO NEW ADMINISTRATION THEY WILL NOT BE AVALABLE MUCH LONGER</div></div>