I just put together a 6.5 Grendel for hunting with a 20 inch Faxon barrel and it really chews up the brass. I have an adjustable gas block and shut it down and put one round in the mag at a time then shoot, open the gas screw just a bit until it locked back with this load. Is it just the way it is for the AR to chew the 6.5 brass? Anything to be done? Thanks for any advice.

Steve............

Sorry I wasn't at home where the cases were at the time I posted but here they are now:

     

Can you post a pic of the damage?

Chews it up where?

As above, posting some pics would be helpful.

Picks added to original post.

Steve..............

First place to look are your feed ramps. Large burrs can do a lot of damage. De burring and polishing is a common fix.
Second place to look is the chamber, it should pass a heaspace check with no forcing. Rough chambers can happen. I have had a few barrels that did not pass inspection. Had to send them back. I polish my chambers but sometimes more is required. I usually do not mess with that and will replace the barrel if possible. I have seen barrel chambers fixed by gunsmiths.
After that extractors can have burrs and chew up the case rim, pretty easy to de-burr those.

6.5 Grendel brass is actually worth a fair bit, its been rare to find in stock. Its worth keeping it in good condition.

My faxon barrel and bolt leave zero marks on my brass.

Looks to be you may have sharp edges on the feed ramps.  Careful work with some emery cloth or VERY careful work with a Dremel tool should take care of that.   Might not hurt work on the undersides of the feed lips of the mags as well.

Hellbender's guide

The neck marks are from the 2:00 locking lugs upon ejection. Normal, but a nuisance.
Scuffs down lower are normal. Scratches may be burrs along the feedramps and chamber entrance.

Thanks guys for the info, that was kind of the culprits I was thinking about but wanted to hear from people smarter than I am.
Thanks for that link it explains a lot.

Steve..........

Well I pulled the barrel and worked on the feed ramp and 2:00 locking lug area and took care of 75% of the problem. I'll work on the ASC mag next and see if that helps any. Thanks again for the fantastic advice and the link.

Steve............

Highly recommend doing the ejector pin modification. Rounds coming from the right side of the magazine has to slide over the pin. The larger case head drags and sometimes causes cases to enter the chamber not straight which can and does cause scratches on the case. All you need to do is take out the ejector and round the square shoulder a little. Made a huge difference in my Grendel.
Search ejector pin mods for an article at Accurateshooter which shows pics.
http://bulletin.accurateshooter.com