Guns per 100 people - Finland 2017: 32.49 (total of 1.79 million) [1] - US 2017: 120.5 (total of 393 million) [2]
All gun deaths - Finland 2017: 138 [1] (~77.09 deaths per million guns) - US 2017: 39773 [2] (~101.2 deaths per million guns) <- A bit higher
Mean death rate per million in mass shootings, 2009-2015 [3] - Finland: 0.132 <- A bit higher - US: 0.089
[1] https://www.gunpolicy.org/firearms/region/finland [2] https://www.gunpolicy.org/firearms/region/united-states [3] https://worldpopulationreview.com/country-rankings/mass-shoo...
The data seems to suggest that the number of deaths and mass shootings sort of tracks with the number of guns, and that Finland isn't particularly better off "per gun".