"Can you show "a right to carry" has reduced crime even a fraction of a percent? "
What you fail to understand is that the guns don't even need to be used. In a society in which only a tiny percentage of people have guns (police- if even they have guns) a criminal has a major advantage if he has a gun. And there is no way to stop criminals from getting a gun if they want one- or they don't even need a gun- a knife or even greater number with fists will work. In a society in which there are many people (say 10 times the number of police officers) who could have a gun, then a criminal is has a problem- every citizen could put out a gun and shoot the criminal. Not only can a citizen shoot the criminal, a citizen has means of disabling his getaway car- so even body armor wouldn't solve the problem. Also a wounded citizen can get medical attention, a criminal can get medical attention, but thereby also goes to jail. Crowds are an advantage to criminals who has a gun and citizens don't, so if citizens have guns, criminals will stick to doing crimes at the nite, when there aren't people around- and this makes it easier for the cops to get them. This adds up to crime not being very profitable, compared to the actual risk.
Personally I wouldn't carry a gun (and I don't own a gun) and I would against laws which require citizens to carry guns, but if say 5-10% of people had guns, then this would be a powerful deterrant to criminals and could allow gun owners to feel more secure about their safety.