I'm not an expert by any means, but I do believe it's laughably easy to get hold of significant weaponry with very little trouble. I know states have different laws, but in many of them (probably over half) it is ridiculous to most people. Including most American's if they bothered to check...
I worked in San Antonio for a few months, I used to frequent a bar called la Tuna, which had a sign up saying no concealed weapons (which I think you need a permit for in Texas). As such, near enough everyone would be sitting about with guns on their hips. As a bloody limey, I found this...