Im running three dsa bolt carriers that were new, and are running with three dsa complete uppers (16 inch and 20 inch) and have yet to run into any problems with them. (approximately 500 rounds per rifle).
"...and which is worst of all, continual fear and danger of violent death, and the life of man, solitary, poor, nasty, brutish, and short."-Thomas Hobbes, Leviathan
...What he meant to add was, "unless, of course, all responsible citizens are armed to the teeth."