HTI Sniper Rifle - Location Overview maps
The HTI is in the Driftwood Islets Region at the Behemoth Defense Area.
It's on top of the tower.
HTI Sniper Rifle - location screenshot
HTI Sniper Rifle - details
L115A3 Sniper Rifle - Location Overview maps
The L115A3 is in the Channels Area at the Auroa Power Plant.
It's in the very top room, accessible from outside ladders and staircases.
L115A3 Sniper Rifle - location screenshot
L115A3 Sniper Rifle - details
Recon-A1 Sniper Rifle - Location Overview maps
The Recon-A1 is on Egg Island at the Bioluminescent Cavern, the cavern where Hill is hiding in the "Point of No Return" Main Mission.
Follow the stream to the end to find the cave entrance.
The box is inside in the first corridor you get to, before opening the door to Hill.
Recon-A1 Sniper Rifle - location screenshot
Recon-A1 Sniper Rifle - details
The Reward for killing Rosebud in the Main Mission.
Zastava M93 Sniper Rifle - Details