To unlock the Laser Rifle, beat the game on Normal difficulty. The Laser Rifle can be used on Hard difficulty.
To unlock hard difficulty, beat Story mode.
"Gunman" trophy hint:
The following is a list of every weapon required to unlock the trophy:
.45 Caliber Handgun (Colt 1911)
9 MM automatic handgun (Glock 18)
.44 Magnum Revolver
1855 Rifle (Colt Model 1855)
Black Powder Rifle (Sharpshooter)
Shotgun (short barrel)
30-06 Auto-Rifle (BAR)
5.56 Rifle (SCAR-L/Mk-17)
Light Machinegun (M249)
Rocket Propelled Grenade
Welcome to the Jungle - Kill 50 Deinonychus.
Woah - Kill a dinosaur during an Adrenaline Burst.
Preparing for the Future - Repair all broken entrances before unlocking the gate.
Pack Hunting - Kill 3 Raptors with one grenade.
Who Needs a Bug Zapper? - Kill 50 Pterosaurs in Rise Above.
Death from Below - Kill a Pterosaur with a grenade.
Blast in the Past - Kill 20 Dinosaurs with grenades.
Plumber Stomachache - Destroy 50 exploding mushrooms.
1-Up - Kill an enemy using an exploding mushroom.
Crispy Critters - Kill 5 Scorpions with the RPG.
Scorpion King - Kill 50 Scorpions.
Chicken Chaser - Kill 50 Velociraptors.
Raptor Extinction - Kill 100 Deinonychus.
Not so Fast - Kill 3 Raptors during a single Adrenaline Burst.
Adrenaline Junkie - Kill 25 dinosaurs during Adrenaline Bursts.
Gunman - Kill a dinosaur using each weapon.
Firepower - Kill 50 dinosaurs using stationary weapons.
Dinomite! - Kill 50 Raptors with a single shot each.
Six Foot Turkey - Kill a Utahraptor.
Outta Nails - Complete any fortification objective without repairing.
Handyman - Complete any fortification objective without the dinosaurs getting in.
Die in a Fire - Killed by fire or lava.
Allergic Reaction - Killed by thorny plants.
Clever Girl - Died in a Raptor Melee sequence.
Mari-Ouch - Killed yourself with an exploding mushroom.
These are not the Hammer - Kill 20 dinosaurs using melee attacks.
What a Prick - Survive a Spinosaurus attack.
I'm the King - Kill a Tyrannosaurus.
Nuck Chorris Rex - Beat the game without dying.
Life Finds a Way - Beat the game.
Hard as Nails - Beat the game on Hard.
Platinum Trophy - Earn all Bronze, Silver, and Gold trophies.