Bans on standard capacity magazines, that is, magazines with a capacity over 10 rounds, are supposed to have an impact on the number of casualties in mass shootings. The question is do they?
The simple answer is no.
As David Yamane reports in his Gun Culture 2.0 blog, criminologist Gary Kleck presented research at the recent American Society of Criminologists annual meeting that studied this question. Kleck’s research looked at mass shootings in which more than six people were killed or wounded. He went with six because that is the capacity of most revolvers and thus no standard capacity magazine would have been needed.
Even with this restrictive definition of a mass shooting, Kleck found that large capacity magazines – defined as holding over 10 rounds – were used in only 21 of the 88 incidents (24%). So, in 76% of the incidents, a large-capacity magazine ban would have made no difference in any event.The bottom line to Kleck's research, as David notes, is that it isn't the tool but the desire of the evil doer to kill as many people as possible. However, this conflicts with the desire of politicians and gun prohibitionists to "do something".
Kleck then goes on to analyze further the 21 incidents in which a large-capacity magazine was used. In every case, the shooters carried either multiple guns or multiple magazines. Therefore, even without a large-capacity magazine, the shooters could easily switch guns or magazines.
Kleck also marshals evidence to show that the rate of fire of most mass shooters is so slow that having to change guns or magazines more frequently would not diminish their casualty counts.