Ammo FAQ:

• What is "Damage Ratio"?
  The Damage Ratio represents the percentage of a round's damage applied to the body. To determine the exact damage of a specific ammo type, visit the firing range, open the ammo selection window, and check the Flesh Damage value. Rounds of the same caliber generally deal the same damage unless their Damage Ratio is above or below 100%.
• What is "Penetration Level"?
  Penetration Level determines how effective a round is at piercing different levels of ballistic vests. Vests of the same rarity color or class will allow 25% Flesh Damage, with the remaining damage absorbed by the armor. If a round hits a vest with a higher class than its penetration level, it will fail to penetrate and deal no Flesh Damage- but will still deal armor damage.
  
• What is "Armor Penetration Falloff"?
  Penetration Falloff is part of the ballistics system that reduces the penetration of a round at range for varying classes of armor. This information can be found on the ammo's "Details" page.