There was a similar situation at our range, and while blown primers are supposed to take the rifle out of action by fragments lodged in the FCG, this guy just pulled the take-down pin after unloading the rifle, inverted it, and "shook the blown primers fragments out on the ground", closed the rifle, reloaded it, and continued shooting!
I later asked him how he did this amazing thing, and he showed me what he called a "rubber lower receiver rug" that fit on the floor of the lower receiver under the FCG. He said they were available from DPMS.
I called the company and no one heard of this item.
Ditto for a Google search.
Has anyone heard of these AR "lower receiver rugs", where can I get some, and has anyone ever used them?
rustymusket