Isn't Wyoming 50th in population? There may be a clue for you...
I would probably agree that population or population density might play a role. But look at this one:
New Jersey has the most gun owners per square mile of any state at 147 gun owners / sqmi. They also have the highest normal population density at 1189 people / sqmi. They are only ranked 21st in the country for gun murders at 2.8 per 100,000 people.
Louisiana on the other hand which is first in the country for gun murder rate with 7.7 per 100,000 people is 23rd for gun owner population density with 46 gun owners / sqmi and 24th for normal population density with 105 people / sqmi.
And New Mexico only has 5 gun owners / sqmi. Yet they rank 13th for gun murders with 3.3 / 100,000.
Not as tight a correlation as I might have expected. Still gotta say there must be something else going on.