Maddog: You may have moved beyond your question, but I've owned a couple of DPMS based LR-308 rifles. They like any AR-15 have to be kept clean and lubed with quality magazines. I haven't buried mine in sand, but have exposed it to rain, dirt, snow and dragging it through the weeds and it has run reliably. Wasn't perfect but most of the failures were related to magazine feeding issues. Both ran reliably with over 400 rounds in between cleanings.

Not sure I'd want to hump this rifle all day. At nearly 11 lbs loaded, plus a combat load of ammo, it would make my M4 look very appealing.