The FBI violent crime stats are interesting.
Under Clinton violent crime dropped 35% in 8 years.
Under Bush it dropped 2% over 8 years.
Under Obama it has dropped 16% in 3 years.
Over that same time period we see a decrease in the number of households with guns.
If we want to correlate gun ownership and violent crime then I guess we could make the argument that if fewer people have more of the guns then the crime rate would drop even more. If one person had all the guns in the US then the crime rate would drop even more.