Comparing countries is somewhat like comparing apples to oranges.
For one, Austrailia population is much lower than US (July 2014 est.) :
US = 318,892,103 VS Austrailia = 22,507,617
http://www.indexmundi.com/factbook/compare/united-states.australia
All European countries combined obviously may have more population but when considering how Europe is broken down into different parts like France, Spain, etc. each behaves like a different society to some extent.
And considering the differences in the cultures, laws, freedom, breakdown, etc. of all those different places, it is not comparing apples to apples.
And its not to say that both Austrailia and Europe have been immune to recent shootings of multiple people. The recent Austrailia Sydney Café hostage situation and Im just reading about today's Parramatta shooting in Austrailia. Europe having the Norway mass murder of 80 and the terrible other mass shootings they have had.
But again, its like comparing apples to oranges because of all the differences. So I don't think you can compare or even claim that they don't have issues just because of their gun laws.