Choosing the right weapons and upgrades in The Callisto Protocol can significantly impact your survival. Since credits are limited and inventory space is tight, knowing which weapons to upgrade and which to avoid is crucial. This guide will break down which weapons to prioritize, how to manage your upgrades efficiently, and which choices will give you the best results in combat.

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1. Avoid Upgrading the Hand Cannon

The Hand Cannon is the first firearm you receive, but it is not worth upgrading. Here’s why:

• It only becomes viable once you unlock Boom Bullets, which requires a massive credit investment.
• Boom Bullets consume nearly an entire magazine per shot, making it inefficient.
• With limited inventory space, carrying extra ammo for this weapon is not practical.

Verdict: Skip upgrading this weapon and save your credits for more effective options.

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2. Max Out the Stun Baton

The Stun Baton is your primary melee weapon and one of the most reliable tools throughout the game. It doesn’t require ammo and is effective in most encounters.

Recommended Upgrades:

• Max out the Damage Tree – Increases melee attack effectiveness, keeping the baton viable throughout the game.
• Upgrade the Blocking Abilities – Helps reduce incoming damage when forced into melee combat.
• Unlock the Heavy Swing Upgrade – This adds a strong finishing attack, useful against tougher enemies.

Verdict: A must-upgrade weapon since it saves ammo and is effective throughout the game.

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3. Max Out the GRP (Gravity Restraint Projector)

The GRP is one of the strongest tools in The Callisto Protocol. It allows you to manipulate gravity, throw enemies into hazards, and instantly kill threats without using bullets.

Recommended Upgrades:

• Max out the Power Meter (Energy Capacity) – Increases the number of uses per charge.
• Upgrade the Recharge Speed – Ensures you can use GRP more frequently.
• Enhance the Velocity – Throws enemies further and makes instant kills easier.

Verdict: Essential to upgrade, as it allows you to kill enemies instantly without using ammo.

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4. Skip the Skunk Gun

The Skunk Gun is a one-handed shotgun, but it is not worth upgrading due to its limitations:

• It has low ammo capacity.
• The Riot Gun (from Danny) is a superior alternative.
• The final upgrade is lackluster compared to other weapons.

Verdict: Skip upgrading the Skunk Gun and focus on the Riot Gun instead.

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5. Fully Upgrade the DK4 Riot Shotgun

This shotgun from Danny is one of the best weapons in the game. It has high damage, a decent ammo pool, and an explosive final upgrade.

Recommended Upgrades:

• Increase Ammo Capacity – Allows for sustained firepower in tough encounters.
• Max out Damage – Increases effectiveness against bosses and stronger enemies.
• Unlock Explosive Rounds – Final upgrade causes bullets to explode, dealing massive damage.

Verdict: One of the best weapons to upgrade, especially for late-game fights and boss encounters.

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6. Ignore the UJC Special Ops Tactical Pistol

This weapon has a burst-fire final upgrade, but it is not worth investing in. It suffers from:

• Limited firepower compared to other weapons.
• High credit cost for minimal payoff.
• Better alternatives exist (like the Riot Shotgun and Assault Rifle).

Verdict: Not worth using or upgrading.

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7. Upgrade the UJC Special Ops Assault Rifle

The Assault Rifle is a lifesaver, especially against the final boss and tougher encounters.

Recommended Upgrades:

• Increase Ammo Capacity – Ensures longer bursts of sustained fire.
• Upgrade Damage Output – Makes it effective against bosses and large enemy groups.
• Unlock Magnum Rounds – Provides a massive damage boost.

Verdict: One of the best weapons for endgame combat, particularly against fast-moving and stronger enemies.

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Final Build Recommendation

To maximize efficiency and survivability, focus your upgrades on the following:

✅ Max out Stun Baton (damage, blocking, and heavy attack). ✅ Fully upgrade the GRP (capacity, recharge speed, and velocity). ✅ Invest in the Riot Shotgun (ammo capacity, damage, and explosive rounds). ✅ Upgrade the Assault Rifle (ammo capacity, damage, and Magnum Rounds). ❌ Avoid upgrading the Hand Cannon, Tactical Pistol, and Skunk Gun.

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Conclusion

With limited inventory space and credits, choosing the right weapons and upgrades is key to surviving The Callisto Protocol. By prioritizing melee combat, using GRP for instant kills, and focusing on the most powerful firearms, you’ll be well-equipped to handle anything the game throws at you.

Stick to this optimal weapon build, and you’ll have the firepower needed to take down even the toughest enemies in Black Iron Prison. Stay sharp, conserve your ammo, and don’t forget to stomp on those corpses!