Nerfs projectile piercing and makes it's chance based more on armour piercing than damage. (#22248)

- Projectiles now lose 30% of their damage for every pierce they go
through by default.

- Ship weapons only lose 5% damage on pierce. 
  
- The default chance was changed from (Pierce Chance (20%) + Damage, to
Pierce Chance (0%) + Damage / 4 + Armour Piercing.
This means the merc's STS, went from 55% chance to pierce, down to 30%,
with reduced damage when it does.

- Specialist anti-tank weapons, such as the PEAC, now have their pierce
chance multiplied by their anti-material potential.
This gives the PEAC 100% piercing chance.


<img width="327" height="261" alt="image"
src="https://github.com/user-attachments/assets/661904ec-3957-4116-a10b-e8a8fc14cd2d"
/>

code/modules/projectiles/projectile.dm

@@ -76,6 +76,8 @@
 	var/pierces = 0
 	///The base chance that a projectile capable of piercing will actually pierce.
 	var/pierce_chance = 0
+	/// 0-1 multiplier, the projectile's damage is modified by multiplying this after each pierce.
+	var/pierce_decay_damage = 0.7
 	///Used to determine whether or not to apply embed chances on hit.
 	var/last_hit_pierced = FALSE
 	/// If objects are below this layer, we pass through them.
@@ -683,7 +685,8 @@
 		return PROJECTILE_PIERCE_PHASE
 	if(projectile_piercing & A.pass_flags_self)
 		if (penetrating > pierces)
-			if(damage > 20 && prob(pierce_chance + damage))
+			if(prob(min(100, (pierce_chance + (damage/4) + armor_penetration) * anti_materiel_potential))) //Base pierce_chance is 0. This gives the STS a 30% chance to pierce once.
+				damage *= pierce_decay_damage
 				penetrating--
 				last_hit_pierced = TRUE
 				return PROJECTILE_PIERCE_HIT

code/modules/projectiles/projectile/bullets.dm

@@ -314,6 +314,7 @@
 	hitscan = 1 //so the PTR isn't useless as a sniper weapon
 	maim_rate = 3
 	anti_materiel_potential = 2
+	pierce_decay_damage = 0.9
 
 /obj/projectile/bullet/rifle/kumar_super
 	damage = 40