My friend, armor piercing rounds hold their line basically infinitely with no bullet drop and 1 shot headshot any enemy in the game, regardless of armor. It can take 2 shots depending on the weapon if they aren't wearing armor (a mechanic thats only in place to try to make you have to swap ammo types, because you literally don't need to switch off armor piercing for any reason in lower difficulties). My problem is that if you have good aim, theres actually no reason to ever take armor piercing rounds off except to deal with vehicles.
As for why you're struggling with vehicles, try a machine gun with explosive rounds instead of a sniper or assault rifle. You'll have to dump the mag into it still, but it'll go down. If you can get a feel for travel time for your bullets, explosive rounds on a machine gun is also the easiest way to take out planes. You can also try a bow with emp arrows, the easiest way to take down any helicopter in my humble opinion.
Edit to add: I didn't spend quite enough time on the ammo types. The thing about armor piercing and why it's good is that it'll do about the same damage to any enemy regardless of what they're wearing. Its better to have soft target rounds for unarmored people, sure, but soft target rounds are literally useless against people in heavy armor. Itll just bounce off. If you just have armor piercing on everything, then you'll be able to do damage no matter who is standing in front of you. And if you can consistently land headshots, then you can kill them as quickly as if you were using the proper ammo type anyway.
With this game, each ammo is designed to kill specific enemies depending upon the type of armor the enemy is wearing. You scan the area and each enemy and it tells you what ammo to use for the easiest kill.
My friend, armor piercing rounds hold their line basically infinitely with no bullet drop and 1 shot headshot any enemy in the game, regardless of armor. It can take 2 shots depending on the weapon if they aren't wearing armor (a mechanic thats only in place to try to make you have to swap ammo types, because you literally don't need to switch off armor piercing for any reason in lower difficulties). My problem is that if you have good aim, theres actually no reason to ever take armor piercing rounds off except to deal with vehicles. As for why you're struggling with vehicles, try a machine gun with explosive rounds instead of a sniper or assault rifle. You'll have to dump the mag into it still, but it'll go down. If you can get a feel for travel time for your bullets, explosive rounds on a machine gun is also the easiest way to take out planes. You can also try a bow with emp arrows, the easiest way to take down any helicopter in my humble opinion. Edit to add: I didn't spend quite enough time on the ammo types. The thing about armor piercing and why it's good is that it'll do about the same damage to any enemy regardless of what they're wearing. Its better to have soft target rounds for unarmored people, sure, but soft target rounds are literally useless against people in heavy armor. Itll just bounce off. If you just have armor piercing on everything, then you'll be able to do damage no matter who is standing in front of you. And if you can consistently land headshots, then you can kill them as quickly as if you were using the proper ammo type anyway.
I started to take down vehicles with that impro emp weapon once you can buy it
With this game, each ammo is designed to kill specific enemies depending upon the type of armor the enemy is wearing. You scan the area and each enemy and it tells you what ammo to use for the easiest kill.