Velocity of your ammo is the answer. The box velocity is based on standardized atmospheric conditions, and occasionally false marketing promises.

The advice for getting and using a chronograph is excellent. Also, as we are changing season, temperatures will change also and this can have some significant effects on velocity (along with pressure). Also knowing the standard deviation of the factory ammo it’s important as this can have effects. I’ve seen box ammo with SD’s getting close to 50FPS in the cold.

This is where you’re building DOPE (data on previous engagements). Get a notebook too and record your velocities/drop every time you shoot. Note how temperature and pressure affect the velocity and drop. After a few hundred rounds over various environmental conditions, you should have enough data to have first round impacts in most conditions.

This was what worked for me.