i was just wonder what the difference was between the AP bullets and buffed damage, because if you can pass through Kelvar in which most Engineers will wear then the use of of AP would be made pointless if Engineers Buffed Damage does more damage to an opponent.
Armor Piercing rounds only negate Kevlar Vests. If the person is not using a Kevlar Vest, then AP rounds do no damage bonus.
Buffed damage increase round damage regardless of if the person has Kevlar equipped or not.
also can you have two buffs at once e.g AP ammo and buffed golden gun
Yep. Your lethality would be quite increased if you were capable of handling armored targets and normal targets alike. But you still won't be overpowered.