Here's a fun "more than zero" way to look at it. The US has had 129 mass shootings since 1982, according to
Mother Jones.
These resulted in 2526 casualties (killed + injured). Over that period of time the US population went from 237 million to 332 million for a naiive average of 285 million people. The average rate is then 4.4 per 500,000.
In Norway there have been exactly two mass shootings since 1982, resulting in 141 casualties. Over that period of time Norway's population went from 4.1 million to 5.5 million, for a naiive average of 4.8 million people. The average rate is then 14.7 per 500,000.
So over the last forty years you're 3 times more likely to have been wounded or killed in a mass shooting incident in Norway than in the US.
Oh but that's just one really bad outlier? Ok fine, what about the rate?
Over the same period those 129 mass shootings average out to 3.2 per year per 285 million people, or 0.011 mass shooting per million people per year. In Norway those two mass shootings average out to 0.05 per year per 4.8 million people, or 0.010 mass shootings per million people per year. So we could say over the same period you're 8% more likely to be in a mass shooting in the US, but 3x more likely to be injured or killed in Norway.
From this my takeaway is that Norwegian mass shooters are slightly less frequent but significantly more effective than US mass shooters.