Unfortunately your juridical skills are too limited to compete with me. So once again here just for you: You have to make a difference between private sales and commercial sales. If you're doing it in a commercial style, especially regularly dealing with new weapons and thousand rounds of ammunition as Steven Steiner alias BayAreaCoins is doing it, you need two things: A license on federal level called FFL, and a registered trade business. I won't cite the legal text for you, go ahead and study it for yourself!