Two rounds trade armor piercing for raw damage: the Special Bullet (S) at ×1.2 damage and AP 0, and the Special Shotgun Shell at ×1.4 damage and AP −1. The armor formula makes both worse than ordinary rounds against almost any armored target. The Special Bullet (S) beats AP rounds only against targets with no armor or armor below 0.4. The Special Shotgun Shell wins only against a target with no armor item at all; against Lv.1 to Lv.4 armor a standard shell deals more. The Special AP rounds of the AR, L, MAG and Sniper calibers have both more damage and AP 6, so they never lose.
The rule
Every hit is multiplied by 2 ÷ (armor − AP + 2), where AP is the round’s level plus the gun’s own AP. When the round’s AP is at or above the armor, nothing is lost. The multiplier is skipped entirely when the target wears no armor, so a negative-AP round loses nothing against armor 0, but against armor 0.25 (a White Lab Coat) the Special Shotgun Shell already counts as 1.25 armor points short.
Worked example against Lv.3 Body Armor (armor 3), shotgun:
| Round | Multiplier | Armor factor | Share of gun damage |
|---|---|---|---|
| Standard Shotgun Shell (AP 1) | ×1 | 2 ÷ (3 − 1 + 2) = 0.5 | 50% |
| Special Shotgun Shell (AP −1) | ×1.4 | 2 ÷ (3 + 1 + 2) = 0.33 | 47% |
| AP Shotgun Shell (AP 3) | ×1 | 1 | 100% |
Where each round wins
| Rounds compared | Armor 0 (none) | Armor above 0 |
|---|---|---|
| Special Bullet (S) vs Standard Bullet (S) | Special Bullet (S) | Special Bullet (S) at 0.01–0.39; Standard Bullet (S) at 0.41–3.99; Special Bullet (S) at 4.01–10 |
| Special Bullet (S) vs AP Bullet (S) | Special Bullet (S) | Special Bullet (S) at 0.01–0.39; AP Bullet (S) at 0.41–10 |
| Special Bullet (S) vs Advanced AP Bullet (S) | Special Bullet (S) | Special Bullet (S) at 0.01–0.39; Advanced AP Bullet (S) at 0.41–10 |
| Special Shotgun Shell vs Standard Shotgun Shell | Special Shotgun Shell | Standard Shotgun Shell at 0.01–3.99; Special Shotgun Shell at 4.01–10 |
| Special Shotgun Shell vs AP Shotgun Shell | Special Shotgun Shell | AP Shotgun Shell at 0.01–10 |
| Special Shotgun Shell vs Advanced AP Shotgun Shell | Special Shotgun Shell | Advanced AP Shotgun Shell at 0.01–10 |
Above armor 4 the Special Shotgun Shell overtakes the standard shell again, but AP and Advanced AP shells deal more than either at every armor level above 0.
Share of damage at each armor level
S rounds (share of the gun’s damage per hit):
| Round | Armor 0 | Armor 1 | Armor 2 | Armor 3 | Armor 4 | Armor 5 | Armor 6 |
|---|---|---|---|---|---|---|---|
| Rusty Bullet (S) (AP -1) | 100% | 50% | 40% | 33% | 29% | 25% | 22% |
| Standard Bullet (S) (AP 1) | 100% | 100% | 67% | 50% | 40% | 33% | 29% |
| Special Bullet (S) (AP 0, ×1.2) | 120% | 80% | 60% | 48% | 40% | 34% | 30% |
| AP Bullet (S) (AP 3) | 100% | 100% | 100% | 100% | 67% | 50% | 40% |
| Advanced AP Bullet (S) (AP 5) | 100% | 100% | 100% | 100% | 100% | 100% | 67% |
Shotgun shells (share of the gun’s damage per hit):
| Round | Armor 0 | Armor 1 | Armor 2 | Armor 3 | Armor 4 | Armor 5 | Armor 6 |
|---|---|---|---|---|---|---|---|
| Rusty Shotgun Shell (AP 1) | 100% | 100% | 67% | 50% | 40% | 33% | 29% |
| Standard Shotgun Shell (AP 1) | 100% | 100% | 67% | 50% | 40% | 33% | 29% |
| Special Shotgun Shell (AP -1, ×1.4) | 140% | 70% | 56% | 47% | 40% | 35% | 31% |
| AP Shotgun Shell (AP 3) | 100% | 100% | 100% | 100% | 67% | 50% | 40% |
| Advanced AP Shotgun Shell (AP 5) | 100% | 100% | 100% | 100% | 100% | 100% | 67% |
What to load
- Targets with no armor item (Koko Koko, Rampaging Arcade, Snow-Bot, Triple-Shot Man, Jeff): the Special Shotgun Shell and Special Bullet (S) are the strongest rounds in their calibers.
- Anything wearing armor: load AP or Advanced AP rounds in S guns and shotguns. A White Lab Coat (armor 0.25) already makes the standard shotgun shell better than the special one; for S rounds the switch comes at armor 0.4.
- Armor break: the Special Bullet (S) strips 6.6 armor durability per hit, about ten times a standard S round. This page assumes armor keeps its full value; against a long fight the special round wears the armor down faster, which these numbers do not include.
The round for every caliber at each armor level is in the best ammo record, and the shots-to-kill calculator compares rounds against a chosen boss.
Sources
- Decompiled game code: Health.cs and ItemAgent_Gun.cs (duckovAPI, October 2025 build)Armor multiplier 2 ÷ (clamp(armor − AP, 0, 999) + 2), applied only when armor is above 0; bullet damage multiplier and AP added to the gun's.
- Ammo pages (Bilibili Duckov wiki, Chinese, revised 9 March 2026)Damage multiplier, AP level and armor break of every round.
Read next
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