Ammo FAQ:

• What is "Damage"?
  The term "damage" on NFAM's ammo guide, linked at the very top of the page, refers to the amount of damage that is inflicted to your PMC when there is no armor to absorb or mitigate any damage from the round. This term could also be called "Flesh Damage".
  
• What is "Penetration" (Pen Value)?
  Penetration, pen., or pen. value all refer to what is called the ammo penetration value. This value determines how efficiently an incoming round will penetrate your armor and how much armor damage will be applied to the inflicted armor piece.
• What is "Fragmentation Chance" (Frag %)?
  Fragmentation is when an incoming round will fragment, split into 2 or more pieces, on impact. When this happens in Tarkov, the round will deal 50% more damage to the impacted entity. Fragmentation chance is currently bugged in EFT and the chances of fragmentation are currently lower than their assigned chance implies. Any ammunition with a fragmentation chance less than 20, will not fragment. 
  
• What does "Recoil" mean on ammunition?
  When inspecting ammunition, the "recoil" value represents the recoil index of that round. This value will either increase or decrease the recoil of your weapon when this round is fired.
• What is Effective Distance? (Eff. Dist.)
  Effective distance is the distance when the fired round has lost 25% of its damage and penetration. It is best to be under this effective distance value when selecting ammunition.
• What does "Maximum Headshot Distance" really mean? (Max HS Dist.)
  This is maximum distance you can instantly kill another PMC with a headshot with this type of ammunition. If the target is over this distance, you may not kill them with a headshot.