It makes good grist for the anti's mill, and a "shocking" story on a slow news night. But would YOU want to test fire one Live at 5? A reporter have to want to be the next Geraldo Rivera and risk having the tragic end of her career played on a constant loop on youtube. I think you'll get few takers. 
FQ13
I would just have the gunsmith do it - besides most journalists would probably have an AD with a factory gun.
*Open with "This is a toy gun available at any sporting goods store. Watch as it can be modified in 60 seconds into an assault rifle that can fire real bullets from this high capacity clip."
**Cut to gunsmith shouldering the rifle and shooting live rounds.
It fits the hysterical drive-by media to a T.