The background check is already pretty extensive, and the beurocracy that handles it is deliberately inefficient (then again, it's government, maybe it just seems deliberate), which typically forces at least a 1 hour wait. Enforcement of existing laws is fine in most cases, but there are some occasions where the law is poorly written, or enforcement is under-funded or poorly supported.
As to the weapons in question, the soldiers of the world carry them. Were we ever to be invaded I guarantee the opposition would have weapons at least as powerful as those you list. The primary purpose of the second ammendment is that the citizens can act in their own defense against tyrrany and invasion. Criminals and terrorists will gladly acquire fully automatic weapons (which have been controlled in this country since 1934, and were not addressed in the slightest by any legislation in recent memory) because they have already made the decision to violate the law. This means that the law-abiding citizen is at an even further disadvantage when defending against such individuals, purely because he obeys the law. All that said, need isn't the issue or germaine to the discussion, liberty is, and I wouldn't deprive anyone else of it merely by owning heavier weapons.
Re: 2nd Amendment
As to the weapons in question, the soldiers of the world carry them. Were we ever to be invaded I guarantee the opposition would have weapons at least as powerful as those you list. The primary purpose of the second ammendment is that the citizens can act in their own defense against tyrrany and invasion. Criminals and terrorists will gladly acquire fully automatic weapons (which have been controlled in this country since 1934, and were not addressed in the slightest by any legislation in recent memory) because they have already made the decision to violate the law. This means that the law-abiding citizen is at an even further disadvantage when defending against such individuals, purely because he obeys the law. All that said, need isn't the issue or germaine to the discussion, liberty is, and I wouldn't deprive anyone else of it merely by owning heavier weapons.