6mm Fat Rat AR with TBAC 30p-1. 20" 1 in 10 Kreiger barrel with Geiselle SSA-E trigger and YHM hand guard. Waiting for the Nightforce SHV scope and this will become my new night hunting rig
Yellowhammer--I apologize for not answering your query sooner, but I have been on a 6-week vacation down in Yuma and just got back about a week ago. I have been busy catching up on mail we had held, getting my income taxes done, and some honey-dos. I know, "give you reasons and not excuses," but that's my story and I'm sticking to it!
Anyway, several posters already answered the question, but YES, that is a mirage shield. This one is made from aluminum and I use Velcro hook material on the barrel and the Velcro loop material on the underside of the shield. The suppressor gets extremely hot and does cause big-time mirage problems. The sun can also cause the barrel and/or suppressor to get quite warm, so the shield keeps the sun off the barrel and helps keep the mirage waves out of you line of sight through the scope.
I actually have the shield on upside down according to the "experts". The "experts" advise you to put the convex side toward the barrel and the concave side up. They recommend that because that way the shield directs the heat sideways and away from the sight line of the scope, while using it the other way the heat waves are supposedly blocked from getting away from the barrel and can "sneak" around the edges of the shield and get into the sight line of the scope.