Since not all DGUs are reported to the authorities and usually do not involve firing the gun, getting a finite number is impossible.
And I guess you can ignore that CDC study they did in 2013, under President Obama's direction. But we all know he's just another NRA shill anyway. 
"CDC Study: Use of Firearms For Self-Defense is ‘Important Crime Deterrent’" - July, 2013
“Self-defense can be an important crime deterrent,” says a new report by the Centers for Disease Control (CDC). The $10 million study was commissioned by President Barack Obama as part of 23 executive orders he signed in January.
The Institute of Medicine and the National Research Council released the results of their research through the CDC last month. Researchers compiled data from previous studies in order to guide future research on gun violence, noting that “almost all national survey estimates indicate that defensive gun uses by victims are at least as common as offensive uses by criminals, with estimates of annual uses ranging from about 500,000 to more than 3 million per year.”
Soooo, my math is a little rusty, but is a low end estimate of 500,000 more or less than the roughly 10,000 murders with guns, a number that continues to fall every year?
Also worth noting, it also kinda gives lie to the gun grabber meme that the CDC is not allowed to do gun related studies, don't it?
But in the end, it's not really about the statistics or piling up stacks of studies funded by Bloomberg, it's about a personal decision to carry for self defense.
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