They're parade rifles and aren't functional anyway. Removing the bolt is another way to make sure that the secret service doesn't need to worry about the military. I wasn't aware that there were direct threats to Obama from the military but why else would this president distrust them?
My parade rifle had a bolt. They were all really loose so they would make a bad *** ringy rattly machinery noise. But the barrel was filed with cement or some kind of adhesive.