AR shell casing scratches

[soonerbb]

My 6.5 Grendel is scratching shell case from the shoulder down, they are about a 1/2 inch long and spaced like the feed ramps. It's every round and very consistent. Had the gas block adjusted by the builder, who has build hundreds of AR'S, (he's out of town). First two outings it was under gassed, could it now be over gassed....Thanks