Nobody uses a sling attached to the barrel to improve accuracy. The major mistake is attempting a precision rifle technique on rifles that are NOT set up to be used that way. Complaints about sling use moving the point of impact on M16's with handguards are really an admission the user doesn't have a clue about what they are really doing. The answer is simple, don't use the sling. The Infantry School taught us to remove the sling in the field, so train like you fight, don't use it on the range. It doesn't shift the point of aim then.
I know single point slings are all the fad, it comes from three gun shooters who transition to pistols. That's a competition range technique. Most soldiers aren't issued pistols, and three gunners - running free floats - also use a rear swivel at the back or front of the receiver, not the front of the handguard.
Lots of the features of the lastest fad - the M4 - aren't for individuals. Think through what you need, if it's looking cool, go for it, but that doesn't justify the actual use for a lot of shooters.
As for the free float and accuracy improvement, there are tubes that can do it lighter. Unfortunately, the whole market for CNC handguards is way overpriced, $200 - 450 for a 1/2MOA improvement is a bit high. A better barrel can deliver that.
