I recently had a problem with the gas tube/key/bcg on my DDM4 V5. It was cycling but I noticed what looked like abnormal wear around the opening of the gas key. Emailed CS and they sent a call tag the next day. Dropped the upper in the mail and it was returned to me good as new less than a week later. They replace the gas tube and the entire bcg. It was all warrantied of course and there were no charges whatsoever, they even pick up the shipping. They also stuck it in a new DD box with a couple of DD stickers. They followed up with a phone call to check that I got it and that I was satisfied. Thought I'd share my good experience with you guys.