Congress can pass any law it wants to and it does quite often. It is the U.S. Supreme Court that is the final arbiter of whether the law holds constitutional muster.
When the constitution was written, Military technology was a lot different. At some point in time, a little common sense needs to be excercised in terms of what is necessary for one to be secure in their self and possesions.
A Predator Drone is not a gun and obviously would not be mentioned in the constitution as it did not exist back then. And certainly not necessaary for self defense. Or to kill coyotes attacking ones livestock. Etc.