Well! You've got a strong topic, now you just need to get your template down. It's an argumentative essay, so you're going to want an attention-grabbing introduction with your thesis statement. You're going to want body paragraphs that explain both sides of the debate, and then try to convince the reader that your side (the federal gov side) is the best position to take. Wrap it up with a conclusion and voila!
One of your points may be that federal power covers all 50 states, meanwhile state gun laws only govern the individual state. Strict gun laws in Illinois don't matter if it's only a two hour drive to Indiana where they have much looser laws.
