In general one usually gets more meaningful results when a) comparing geographically and/or culturally similar countries for things like these. E.G the UK has half the mortality rate of the US, Canada and the EU have 2/3 of the US rate. And b) compare trends, not single values. E.G. US rates are rising (which I as a layman would interpret as speaking against the firearms thesis), while the rates of Lithuana and Japan are falling.
