I do want to point out that all weapons do get a boost from Penetrator perk, as it adds additional armor penetration for any range weapon (and spears). So a point in Penetrator gives you a 10% increase in armor penetration for all guns (20% for spears).
So AP ammo starts with a 50% armor penetration that you can increase with the Penetrator perk. Max would be 70%. Maxed out at Perk Level 3.
Spears, if you were to max out Penetrator perk, would give you a 100% armor penetration. Maxed out at Perk Level 4