In 1993, before nearly all US Congressional Representatives and Senators traded in their vertebrate status on the issue of gun control, Senator Pat Moynihan from New York suggested that the emphasis on gun control should be on bullets, not guns (see here for some history). His reasoning, based on the principle that bullets, not guns, kill peopl, was quite sound. Since guns are nearly indestructible and the supply in this country could last hundreds of years, getting control over the weapons is essentially impossible. On the other hand, the supply of ammunition (at least at that time) was only three years. Moynihan's solution, expanded upon by the comedian Chris Rock (see link above), was to substantially raise taxes on ammunition, not on the target shooting variety, but on the bullets designed to kill with maximum damage (e.g., hollow points).
Clearly, any effort to control gun sales should be implemented. If we can't eliminate them for legal, political or practical reasons we can at least control them. Re-instituting the ban on assault rifles would be a good start as would limiting the size of gun clips. However, the advantage of focusing on the control of ammo sales is even better. Here's where a little biochemistry provides a lesson or analogy:
In biochemical pathways of metabolism - for example, of the sort that breakdown foodstuffs into energy - the enzymatic steps in the process that have the highest turnover or throughput are generally those where control over the pathway/process as a whole is best accomplished. Similarly, if the turnover (lifespan) of guns is slow, but the turnover (lifespan) of the bullets is fast or faster, then it makes sense to focus control efforts on the bullets.
Making bullets more expensive limits their availability economically, although it's not clear how expensive they would need to be and how much tax could be imposed on them. Background checks for the purchase of ammo could also help control their sales. Following on from the biochemistry lesson above, however, there is another way to control the turnover of ammunition: require that gun powder include an ingredient that would make it ineffective over a relatively short (2-3 years) period of time. A time-release self-destruct mechanism. This would be analogous to denaturing alcohol to control the distribution of that substance.
Requiring ammo to have short shelf-life would magnifying the effects of a hefty tax on bullets and background checks for it purchase. Of course, this wouldn't stop gun deaths - people might be able to make their own gun powder, for instance - but it should reduce it.