There are barrel nuts then there are barrel nuts, and not all are created equally. We tested and evaluated a lot of hand guards to find ones that did not allow or cause the barrel nuts to loosen up.
As some of the guys pointed out, just because folks CAN put their own rifles together, it doesn't mean they should. I have been trained by two different manufacturers as an armorer and there are key checkpoints that have to be verified before a rifle can go to test and be shipped.
Carbon fiber hand guards seem like a good concept, until you see things like this. High quality carbon fiber hand guards tend to be quite expensive. Low end carbon fiber hand guards are disastrous jokes and don't save you much in weight versus a good quality aluminum hand guard.
