316 shootings per day, every day for 7 years, is 807,380 people shot. 807,380 into 331,000,000 (the US population) is one in 400. Therefore if the US population were 400 people, there would be one person shot every 7 years.
I think your math is off there. First, you're forgetting that there's 365 days in a year. Then you're forgetting that the scale is 400 people. Yours basically said that shootings irl are only happening once per year instead of once per day, and the US pop is only 1 person.