If you're going to calculate the projectile effect and range you'll do it in accuracy shooting like a 
sniper would do, not with a "bump stock" which deteriorate accuracy and point of aim.  Heck, he  didn't have to know the exact distance and elevation with that  big a target (a crowd of 22,000 people bunch together) just spray and pray.  I  don't know what is in his note but I'm thinking logically perhaps what he wrote down was something else all together.