Can anyone provide a reason for more than 3 rounds?

[geckosfeet]

61. There are several reasons. Link herein.

Many plinking and target pistols use 10 round magazines. The majority of the more expensive pistols have 5 round magazines.
Bullseye (shooting competition)

This is an interesting report on firearms discharges for the NYPD. It is a pdf.

NYPD Annual Firearms Discharge report

. . a single incident can significantly skew averages. For this reason, with small samples, the mode can be most revelatory [see Figure A.10]. The mode for the number of shots fired by police is one.

The chart is on page 8. In 27% of incidents 1 shot was fired. In 15% two shots were fired. But I can guarantee you - none of the officers involved in any of those incidents would have wanted to be carrying any less ammunition in their magazines. Neither would any private citizens who were forced to defend themselves.

There are some states (MA is one) that already restrict possession of magazines that carry more than 10 rounds. I'd say look to those states. Evaluate the effectiveness of their firearms laws, and go from there rather than trying to get legislators to implement unproven proposals.

One of the things that the 1994 Federal Assault Weapons Ban attempted to do was ban high capacity magazines.

Federal Assault Weapons Ban

The Act also defined and banned 'large capacity ammunition feeding devices', which generally applied to magazines or other ammunition feeding devices with capacities of greater than a certain number of rounds, and that up to the time of the Act were considered normal or factory magazines. Media and popular culture referred to these as 'high capacity magazines or feeding devices'. Depending on the locality and type of firearm, the cutoff between a 'normal' capacity and 'high' capacity magazine was 3, 7, 10, 12, 15, or 20 rounds. The now defunct federal ban set the limit at 10 rounds.

During the period when the AWB was in effect, it was illegal to manufacture any firearm that met the law's flowchart of an assault weapon or large capacity ammunition feeding device, except for export or for sale to a government or law enforcement agency. The law also banned possession of illegally imported or manufactured firearms, but did not ban possession or sale of pre-existing 'assault weapons' or previously factory standard magazines that were legally redefined as large capacity ammunition feeding devices. This provision for pre-ban firearms created higher prices in the market for such items, which still exist due to several states adopting their own assault weapons ban.

When the law was being written, certain manufacturers ramped up production of magazines, knowing that if they were produced BEFORE the ban went into effect (pre-ban magazines) that these items could still be sold legally. The net result was that there are still an abundance of them available, even in states that adopted the ban on higher capacity magazines.

There are some states (MA is one) that already restrict possession of magazines that carry more than 10 rounds. I'd say look to those states. Evaluate the effectiveness of their firearms laws, and go from there rather than trying to get legislators to implement unproven proposals.