Reduced magazine capacity was part of the Federal1994 Assault Weapon Act, too.  Only a 10 round magazine.
 
"A 2004 critical review of firearms research by a National Research Council committee said that an academic study of the assault weapon ban "did not reveal any clear impacts on gun violence outcomes".  
 
And that "The Jerry Lee Center of Criminology, University of Pennsylvania found no statistically significant evidence that either the assault weapons ban or the ban on magazines holding more than 10 rounds had reduced gun murders. However, they concluded that it was "premature to make definitive assessments of the ban's impact on gun crime," and argue that if the ban had been in effect for more than nine years, benefits might have begun to appear."

You are trying to re-invent the wheel even though it has a flat tire!