Side-mission: Operation Phoenix
Collectible weapon #13: HVR (SMG)
Soon after beginning Operation Phoenix, follow Salter through the asteroid field until you see an SDF carrier appear in the distance. Two troopers will emerge. Kill them both and track where their weapons float away to (remember, you’re in zero-g for this mission). One of those yellow-highlighted weapons will be the HVR.
Side-mission: Operation D-Con
Collectible weapon #14: Ballista EM3 (heavy)
While in the latter part of the mission, you’ll hear the words “The infirmary should be close, sir.” As you do, you should see an ammo crate to your left - go down the fiery corridor the ammo box is on and just before the door at the end you’ll find a hackable door to your left. Hack it, open it and the Ballista EM3 is yours for scanning.
Side-mission: Operation Deep Execute
Collectible weapon #15: Eraser (heavy)
During this mostly covert side-mission you’ll be tasked with entering a factory floor to find and locate a set of credentials for a technical officer. Before you head over to him, turn immediately as soon as you enter the area and you’ll find a door that needs hacking. Don’t worry though, you’re in disguise so you won’t get rumbled. Open the door when it’s finished and you’ll find the Eraser on the table.
Collectible weapon #16: RPR Evo (SMG)
RANDOM ALERT: The pint-sized but powerful RPR Evo SMG (in all its variants) is a top-notch weapon to have at hand, so why not add it to your personal armoury? This is another randomised gun appearing in any main or side mission containing SMGs. We discovered ours in the armoury with the weapon sample found at the end of Operation D-Con.
Mission: Operation Burn Water
Collectible weapon #17: Spartan SA3 (heavy)
As soon as the SDF C12 drops down in the square courtyard, immediately run over to the platform to the left. Thrust jump up onto the platform and you’ll find the Spartan SA3 leaning against a set of crates. Be quick as the big bot will target you soon after.
Collectible weapon #18: Banshee (shotgun)
RANDOM ALERT: As with all the other randomised weapons in the game, the deadly Banshee shotty can be found across any mission where enemies are toting shotguns (this is most of them, but we managed to discover one while playing through the Operation D-Con side mission above Venus). As usual, this weapon is available in both main and side missions.
Mission: Black Flag
Collectible weapon #19: KBS Longbow (sniper)
During the Prisoner Escort section of Operation Black Flag, you’ll pursue the SDF prisoner into a shop where a bot is stood outside on top of a van - you’ll know it because Reyes says “Shit!” the moment he sees all the SDF troopers. Run to the right, jump out of the window and you’ll see the KBS Longbow leant against a doorway. There will be a cart right in front of it.
Collectible weapon #20: Oni (handgun)
As soon as the Trap Sprung section of the mission begins (where you eject from your Jackal and boost into a hangar of the Olympus Mons) go forwards into the shell of a rectangular container. On the floor next to a rifle will be an Oni handgun.
Collectible weapon #21: Erad (SMG)
Now while this next weapon has a nearby fixed location, you’ve almost certainly come across it before as its one of the most commonly generated weapons. Still, if you haven’t picked one up in your travels, go through the container that contained the Oni, turn left and head towards a staircase. Beside said staircase is an Erad SMG.
Collectible weapon #22: Titan (LMG)
The final weapon can be found in one of two places from the beginning of the Trap Sprung section of the mission, but if you’ve just collected the Erad from the bottom of the stairs, turn 180-degrees and you’ll find it laying against some white crates, Alternatively, you can find one right next to the fixed Oni.
Congratulations - you've scanned all 22 collectible weapons and earned the Gun Nut trophy or achievement. Good job, soldier.