Originally Posted by
SA Friday
The hand guard is your barrel nut. Your barrel nut is what holds your barrel in your upper securely. I've seen two off-brand hand guards in the last three years that had shit barrel nuts and the barrel was moving. It's a complete pain in the ass, but rebuild the upper with a different barrel nut and test it. I've tried to come up with a test to show how much a barrel nut is mating up with the barrel extension collar, but so far, it's just easier to rebuilt it with a reliable test hand guard and barrel nut.