Could not be more happy with my experience with MAS Defense (www.masdefense.com). Ordered a custom upper to go on my lower. You submit a request for a build and someone reviews it to make sure everything will work. The builder informed me the handguard I chose would not cover the gas block, so I chose one that would. Took about 4 business days to complete assembly/test fire and get in the mail, 3 days shipping via USPS (even tho I paid for 2 day priority).

Initial quality was excellent. No tool marks anywhere from assembly, everything was nice and tight. Pinned on my existing lower as expected. Accuracy was top notch, zeroed right in and held a 10 shot group under 1" @ 100 yards. With a scope and off a tripod using hand loaded 55gr bulk hornady bullets. Even better was that a few other folks at the range said it looked like a "multiple thousand dollar custom rifle".