According to a 2008 analysis of NYPD firearms discharge data done by the New York Times, between 1996-2006 officers hit their intended target about 34 percent of the time.
Another analysis, published in 2006 by the RAND Center on Quality Policing at the request of Police Commissioner Raymond Kelly, found that in the years 1998-2006, the average hit ratio for officers involved in a shooting where the subject does not fire back was 30 percent. During a gunfight, where the target is shooting at officers, the study reported that the hit rate falls to just 18 percent.
The Times reported that in 2006-2007, Los Angeles police officers hit their targets between 27 and 29 percent of the time, respectively. There is no reliable national data on hit ratio. http://www.cbsnews.com/8301-504083_1...shot-accuracy/
Those statics mean that if you shot at one bad guy with a 10 round magazine, you will hit him 3 times if you shot as well as a police officer when the assailant is not shooting at you. If they are shooting at you, you only hit him 2 times out of 10 if you are equal to a cop.
A recent incident had a lady shoot a robber 5 times in the head and neck with a .38, and he was still functional. He drove away. A 10 round mag is not enough to ensure survival against multiple assailants. Or even one determined one.
So, even if the 2nd amendment were about self defense, 10 round mags are a bad idea.
The 10 round limit will not hamper a spree killer, they will just wear a tactical vest with a lot of mags or use an illegal one. I bet they don't mind breaking another law. I can change one out in a second or so with out even lowering my weapon. However, when someone breaks in, I will not have time to gear up. I will have to use what is in my weapon. You can bet I want more than 10 rounds when the lives of my family are riding on my defensive capability. The same thing applies on the street. I am better off drawing a pistol that has enough ammo for the job with out reloading.
I bet Obama's secret service agents have more than 10 rounds in their weapons. Even Bloomberg's 5 full time body guards have more than 10 rounds in their pistols. Heck, even the full time guards in the private school his daughters go to have full size magazines. And those guards are not secret service. They have been there for a long time.