For the first 3 duels:
Pistol - 1 hit: 24, 2 hits: 48, 3 hits: 72, 4 hits: 120, 5 hits: 168 (1 win needed versus chest)
Rifle - 1 hit: 30, 2 hits: 60, 3 hits: 120, 4 hits: 180, 5 hits: 200 (2 wins needed versus chest)
Scar - 1 hit: 38, 2 hits: 76, 3 hits: 152, 4 hits: 200 (3 wins needed versus chest)
For the last 2 duels:
1 win - healing
Both wins - shield (extra health, you can have up to 100 health and 100 shield)
All 5 wins and the chest will instead drop an OP weapon:
Sniper - 1 hit: 74, 2 hits: 148, 3 hits: 200