Would it be better if one group of federal laws governed firearms?

Actually, federalism works pretty well as is: federal law is restricted to some degree by second-amendment constraints, and states/localities have a degree of flexibility on further restrictions. I'd suggest that federal law as it currently stands is a bit too restrictive, and more of the lattitude should be left to state and local governments. But an over-arching country-wide law could be even more onerous than is now the case, so be careful what you wish for. This applies not only to firearms, but to most other aspects of government, as well: some powers are granted to the central government, others retained by the various states or the individual citizens. It's a basic principle of our government.