1. Get a 9x21mm weapon.
2.Fire and hit a normal human target until it is neutralized.
3. Fire at long range and observe bullet drop.
4. Repeat 1-3 with a .45 caliber weapon.
5. Observe that there is no reason to use the 9x21mm over the .45 and that it's seems the 9x21mm performs like a 9x19mm or perhaps even a 9x18mm round.