WOW Ernie that's a monster, I did not see the weight but I'm going to guess 13lbs?
On the SBR thing I don't think this in any way qualifies, no matter how inept an ATF agent may be. There are just to many factors involved, Ernie would literally have to insult the agents mother to her face (I don't see him doing that) and then he would only be gotten on a very long stretch of a technicality after all other charges were filed it would be dropped. Not to mention they do not consider the grip on the MSR, AUG or the TAVOR to be a forward vertical grip, kind of silly to even bring it up.