I'm not DPMS but I have a Tuber,
AFAIK its a HBAR freefloated in their handguard, just cut a little bit longer. Then they put a cap on the end. If you shoot rapid fire it can get really hot. After 2 20 rounders were bumpfired down range, it got VERY hot, hot enough that the M203 handguard was the only way to handle it, and I think I loosed the adhesive on it too. (Not a bog concern to me, I need to take it off to attempt to mount a rail for a vertical grip, and it is on there VERY snug).
I might see if I can get the top little indent or three cut out for ventilation while maintaining the look.
:) Glad you like my rifle.