It seems that that data gives statistics for a single year, and not the same year for each country. While the annual gun-related death rate may be somewhat stable for the U.S., I would guess it varies a lot from year to year in smaller countries depending on whether there was a major incident that year or not. I'd want to look across a similar-size population (e.g. all of EU) and (say) a 10 year span, and then calculate #deaths/year/1,000 population