Citizens lobbying for a shall-issue law in Maryland have an interesting page with statistics on it. Here’s a choice one:
In Florida, where 315,000 permits have been issued, there are only five known instances of violent gun crime by a person with a permit. This makes a permit-holding Floridian the cream of the crop of law-abiding citizens, 840 times less likely to commit a violent firearm crime than a randomly selected Floridian without a permit.
Several other states have a 0% rate.
I also ran down the numbers for a conversation I had about the general number of violent gun crimes in the US.
According to gun-control groups, the death rate in the US attributable to guns is 10/100,000. Of that, the homicide rate is 38%. Of homicides, those attributable to non-relations/friends (random criminals) is 41%. If you multiply that all together, the odds of being killed by a stranger with a gun is about 1/25,000. The odds of being killed in a car wreck is 1/18,000. The odds of being killed by lightning is far higher – this is fairly common, as things go.