When he gets down from The roof, there is some sort of loose clothing like a jacket or maybe that's his bag that he's carrying in his arms.
Every once in a while, you can see the barrel poking out from the loose Jacket.
He was using whatever cloth item to slightly conceal his rifle, and was allowing the barrel to poke out at times.
In the preshooting other video, he's limping because the rifle is going down his leg. He can only bend his leg so much. Ask anyone that's been in a knee immobilizer what it's like to walk.
"I wanna go home with the Armadillo."- Gary P. Nunn