Just got to this post late. FF tubes pretty much keep anything from effecting the barrel giving it a more true point of impact. I have one on a S&W M&P 15 and love it. Many people get tight into there slings and when teh sling is mounted to the barrel it effects it even more. So now the thing to do is get a FF hanguard and attach the sling onto it as to not throw of the point of impact. If you put stress on that barrel you get unusual wear patterns in the barrel as well. I have another AR without FF tubes and my dad even has a 1st Gen AR with the rotary rear sight and the triangle hanguards and I will say I am accurate with all of them, but I have heard of accuracy increasing as much as 50% with them. I have gone 10 for 10 at 500 yds with an M16 A2 so like I said I dont notice it severely but I'm just an AR guy. There is a purpose to them though and it makes a difference for some guys.