Importance of Quality Parts from Reputable Companies
When I was cleaning my AR, I dropped the bolt carrier on the gas key bending it. I couldn't get it straight enough to work, and Bravo Company was out of stock, so I headed down to the local gun show and picked up a key and screws.
Looking at it, it looked like it was good quality. It was chromed inside and parked on the outside. I took it home and installed it according to the directions in the Marine Corps manual and went shooting. The first time out the gun ran fine but I didn't have time to fire many rounds. The next time out it ran fine for a few magazines but after that it failed to cycle every five our so rounds.
I brought it home and compared the key installed to the one on an LMT carrier. At first I didn't notice anything different, then I inverted a can of compressed air and blew it through both keys. On the LMT carrier, most of the air blew out through the carrier. On my carrier most of the air blew back out through the key. Looking inside both keys with a flashlight, I discovered the key I had boght was missing the shoulder inside that the LMT carrier had.
I stopped by Rainier Arms and picked up a carrier key take-off and installed it. The next time out I ran over 400 rounds through the carbine with no failures of any kind and all the rounds dropping into the 5 o'clock area.
Moral of the story? Don't take any chances. Buy quality parts from reputable companies.