In the US, state by state, there is no correlation between gun ownership and the murder rate
For example, the District of Columbia has the lowest gun ownership rate(3.7%), but the highest gun murder rate of the 50 states and D.C.(16 per 100,000) Wyoming has the highest gun ownership rate(59.7%), but the 7th lowest gun murder rate at 0.9 per 100,000(behind Iowa, Idaho, and Utah who tie for 6th at 0.8 per 100,000). The gun ownership rates in those three states respectively are 42.9%(16th highest gun ownership rate), 55.3%(6th highest gun ownership rate), and 43.9%(14th highest gun ownership).
This is just to give you idea there is no statistical correlation between gun ownership rate and the gun murder rate on a state by state basis.
Gun violence in the United States by state - Wikipedia the free encyclopedia
If you actually look within the countries of the Western world, there is no correlation between the gun ownership rate and the gun murder rate.
For example, if we look at table six in this Harvard Study I will link below, Czech Republic has the highest gun murder rate at .92 per 100,000, but about 27 guns per 100,000 in the population, whereas Finland and Sweden have respective 411 guns person 100,00 in the population and 246.65, and have respective gun murder rates of .87 per 100,000 in Finland and .31 per 100,000 in Sweden.
http://www.law.harvard.edu/students/orgs/jlpp/Vol30_No2_KatesMauseronline.pdf