The US has 260 or so million guns, or just 25,000 per annual gun death. Why is the US five to eight times as efficient at killing people with guns? Is it that we have better targets, escalate disputes better, or have more drug wars?
It's the total number of lives - the actual human beings - that's important, not the completely meaningless and artificial metric you just came up with.
We still had almost 11,000 deaths from gun murders during that particular year, more than all the American servicemen and women who have died in both Afghanistan and Iraq combined
since 9/11. How many guns exist in the total population per gun murder means absolutely nothing. You might as well have mentioned invisible elephants or Mogwai and it would have been just as valid.