Arm or Ally had Aero Precision EPC parts in stock when just about no one else did, and at much better prices. Wish I had known about them before ordering my upper assy. from AP; could have saved over $120. I'll be a return customer for sure! Update! Went to fire my newly assembled weapon and had two rounds fail to fire; didn't even contact the primer. I checked to make sure I didn't do something wrong during assembly and couldn't find anything, so I submitted a trouble ticket to AP. It's been 5 days, and I haven't heard anything back. Not sure how long they usually take but 5 days seems long. I'll give them benefit of the doubt, but 5 days does seem long.