Perform the following actions to unlock additional guns.

Pesticide Cannon / Tier 8 Rocket Launcher - Achieve Rank 8 with the Trooper Armor.
Pesticide Missile / Tier 8 Missile Launcher - Achieve Rank 8 with the Tactical Armor.
Pesticide Mortar / Tier 8 Grenade Launcher - Achieve Rank 8 with the Battle Armor.
Pesticide Rifle / Tier 8 Sniper Rifle - Achieve Rank 8 with the Jet Armor.