Bloomberg News reports:

Illinois Representative Rahm Emanuel, chairman of the House Democratic Caucus, said the top priority of his party's lawmakers is hiring more police to fight crime, not tougher gun control.

Emanuel said the House "might" or "might not" re-enact an assault-weapons ban that expired in 2004. That legislation, which limited the capacity of handgun magazines, would have reduced the amount of ammunition used in a shooting rampage that killed 32 people this week at Virginia Tech University.

Setting aside the various other questions raised by assault-weapons bans, how can a news service say with a straight face that legislation limiting the capacity of handgun magazines would have reduced the amount of ammunition used by the murderer?

Recall that semiautomatic handguns are reloaded by popping out a magazine, popping in a new magazine, and chambering another round. If the shooter has preloaded several magazines — which the Virginia Tech murdered had — the process can take a second or two, even with no special training.

Banning 15-round magazines (which the Virginia Tech killer apparently had) and limiting magazines to 10 rounds — as per the expired assault weapons ban — or even to 6 rounds, would thus simply require the shooter to reload a little more often. This may limit a shooter who is in the middle of a firefight when one is shooting very quickly (6 to 10 rounds in a few seconds), but not a shooter engaged in a mass shooting such as this one, which took place over many minutes. It doesn't seem even very plausible that a smaller magazine size would have led to fewer shots being fired. It is certainly wrong to say that it would have reduced the number of shots (even if one recognizes that "would have" represents very high probability rather than just certainty).

This is a classic policy analysis mistake, but one that I've found particularly common in gun control debates: assuming that when one enacts a law, that will change the subjects' behavior in the way the law contemplates, but with no compensating substitution effects. Sure, if by reducing magazine size, we get someone to load 4 10-round magazines rather than 4 15-round magazines, he'll have fewer rounds he could readily shoot.

But why on earth would we think that this is how people will react? Why wouldn't they just load 6 10-round magazines instead of 4 15-round magazines? (Another classic policy analysis mistake is simply not knowing the technical details of the items that one is discussing; my sense is that many people, likely including many reporters, just don't know how quickly one can switch magazines on a semiautomatic, or don't even know precisely what a semiautomatic is.)

I should say that banning semiautomatics altogether, and requiring handgun users to rely on revolvers, might theoretically have more of an effect; reloading a revolver does take somewhat more time. It's not vastly more, and if one has a backup gun handy, one won't even be particularly vulnerable while reloading the revolver; and there are other problems with the proposal, including the political problem that the ban would affect weapons that are owned by tens of millions of gun owners.

But at least there'd be something potentially plausible to talk about there. There is, on the other hand, no credible defense for the claim that "[the] assault-weapons ban that expired in 2004 ..., which limited the capacity of handgun magazines, would have reduced the amount of ammunition used in a shooting rampage that killed 32 people this week at Virginia Tech University."

UPDATE: In the original post, I described the process of replacing a magazine as removing the empty one, loading a full one, and then possibly chambering the round, unless one reloads while there is still a round ready to shoot. On reflection, I realize that one would almost always wait until all the rounds have been used before putting in the new magazine, so I changed the post to say that replacing the magazine requires removing, loading, and chambering. The bottom line is unaffected; reloading can still take a second or two, without any fancy training.