Ranged item maths

im a bit confused about the maths behind the ranged items
 

https://imgur.com/a/XGpThIu

Red - Bullet power (speed of projectile therefore effecting arc & effectively range)

Blue - Bullet damage

But its not this simple it appears there seems to be some sort of calculation for the final damage
With the shown screen shot the output damage of the item is 8
 

https://imgur.com/a/bqHnOJI

Yet once I input this the final damage output of the item is 33

Is there an easy way to work out this so i can determine the damage before hand?