Don't mourn the political demise of Senator Dianne Feinstein’s assault weapons bill.

Here’s why.

The philosophy behind an assault weapons ban is that there are two kinds of rifles. One kind – the sportsman’s rifle – is designed for hunting and target shooting. It is about accuracy. The rifleman places the stock against his shoulder and looks through a pair of sights mounted along the top of the barrel. He fires a shot, and then – because the recoil has changed the position of the rifle – re-aims before firing another shot. The other kind of rifle – the assault weapon – is designed for warfare. The shooter points rather than aims, and sprays as many rounds as possible in the general direction of his target. This weapon may have a pistol grip to make it easier to hold at the waist. It may also have a barrel shroud – a covering with ventilation holes that surrounds but does not touch the barrel. The barrel shroud gives the shooter a place to grasp the front portion of the gun with one hand while at the same time allowing the barrel to cool. (When firing multiple rounds, a gun barrel becomes too hot to hold, and a fully-enclosed barrel could become hot enough to melt.) Senator Dianne Feinstein was also concerned about two other attributes of assault weapons: a collapsible stock, which allows a long gun to be folded up for concealed portability; and a threaded barrel, on which one could screw on a silencer or a flash suppressor, so that one could fire at night without having a muzzle flash give away his location.

But all of these features – barrel shroud, pistol grip, collapsible stock, and threaded barrel – are merely ancillary to the key feature of an assault weapon: the high-capacity magazine. Today magazines of thirty rounds are common. This allows someone shooting a semi-automatic rifle of any design to fire thirty rounds before reloading. Magazines holding ninety rounds are also readily available. A weapon is semi-automatic if one must pull the trigger to fire each round, while an automatic weapon continues to fire as long as one keeps the trigger depressed. While private citizens may not lawfully possess automatic weapons, the distinction is less important than one may think because a shooter can fire more than a round per second using a semi-automatic weapon. The vast majority of guns sold in the United States today are semi-automatics; that includes sports and hunting rifles as well as guns classified as assault weapons.

The single most important thing than can be done to complicate the work of mass-murderers is to prohibit high-capacity magazines. Everything else pales in importance.

Focusing on the ancillary features of assault weapons allows gun control opponents to argue that the distinction between sporting guns and assault weapons is largely cosmetic. Even the collapsible stock is becoming less significant as so-called assault pistols grow in popularity. In addition, focusing on the cosmetic – and arguably psychological – aspects of assault weapons made sportspeople who liked to shoot such weapons feel demonized.

Moreover, Senator Feinstein’s bill grandfathered existing high-capacity magazines. This would have allowed people to stockpile and continue to use high-capacity magazines for decades. A similar grandfather provision was the Achilles heel of the original (now expired) assault weapons ban, rendering it largely ineffective over its ten-year life span.

From both public policy and political points of view, it is wiser to focus exclusively on the key feature of weapons of war: the high-capacity magazine. Private citizens should not be able to possess gun magazines – whether for rifles or pistols – that hold more than a certain number of rounds. In my judgment, five-round magazines are adequate for self-defense, hunting, and target shooting. Legislation recently enacted by New York State set the limit at seven rounds. The original federal assault weapons ban had a ten-round limit. A smaller limit is better. One can remove a spent magazine and replace it with a fully-loaded magazine very rapidly. Someone using a gun for self-defense or for sports purposes can have several fully-loaded magazines, and change a magazine after firing, say, five rounds. But having to do this repeatedly complicates the work of mass-murderers. To fire ninety rounds, someone using thirty-round magazines must replace the magazine twice. Someone using seven-round magazines would have to replace them twelve times. Someone using a five-round magazine would have to replace them seventeen times. Jared Loughner, the mass murderer in Tucson, was tackled while he was attempting to change magazines.

Does having to change magazines more frequently inconvenience sports shooters? Sure, but it’s a minor inconvenience, and reasonable and responsible sportsmen and women fully understand that public security must trump recreational convenience.

So don’t mourn Senator Feinstein’s assault weapons ban. The political costs always outweighed the public policy benefits. Under the present political climate, its demise was inevitable. We should focus on prohibiting high-capacity magazines and ignore the ancillary attributes of assault weapons. And we must not exempt existing magazines; it’s important that high-capacity gun magazines be removed from general circulation. Magazines are relatively inexpensive – about twenty dollars each – and can be replaced far more easily than guns themselves. Once we are talking about magazines only, the need for a grandfather provision diminishes.

Some gun control advocates are misled by polls (such as this one by the Pew Research Center) that show current support for an assault-weapons ban to be as strong as support for a ban on high-capacity magazines. But what's important is not where the polls stand today; it's where they can stand after a sustained public education campaign. The case for restricting high-capacity magazines is simpler, clearer, and stronger from a public policy standpoint. Americans can be persuaded that this will really matter.    

And, of course, we need universal background checks for all gun sales, which is something the American public already overwhelmingly favors.

For purposes of public education, and developing the overwhelming political support necessary for enacting gun control legislation, it’s important to advocate a few simple, easily-understood proposals and explain over and over – in as long and sustained a campaign as necessary – why they are sensible.