In USA 48% of the households have guns USA have about 9 murders per 100 000/habitant 6,3 of them with guns.
In Australia 20% of the households have guns Australia have 1,9 murders per 100 000/habitant 0,4 of them with guns.
So 66% of the murders in USA involving a gun the number for Australia is 21%.
Not only do USA have a much higer number of total murders/habitant also the percentage envolving guns is much higher
Here is a chart
I would also like to say that I have seen studies saying that a law against guns will not in the short run change theese numbers probably because it is already so many guns in the social system.
Also the murder rate in USA went down for a couple of years but the guns have at the same time increased, the percentage of gun envolment is however the same.
Also about punishment systems, USA has one of the hardest (if not the hardest) punishment systems in the western world.
But still has the highest numbers for homicide and violence.......
This is statistics and can be interpreted any way you want, but I dont think US citicens like to murder more, than people in Australia for example.
So what is the diffrence social ? access to guns ... ? lack of education ? you tell me.