Regina's starting weapon at the beginning of the game, in the game Manual it says the weapon is a "Standard 9mm handgun". This weapon is completely fictional. Most of it's overall design seems to be made from a mixture of the Desert Eagle, H&K MK 23, and maybe even some elements from the Glock 17 and Browning Hi-Power MK III.
Unknown Shotgun
A Dead Drug Store Clerk in the Edward City Chapter can be found in-game with an unusable shotgun laying next him. The overall appearance of the shotgun, hints to a short barrelled compact pump action with the receiver and pistol grip matching that to either a TOZ-194 or a Pistol gripped Mossberg 590 "Compact Cruiser".
SPAS-12
A Franchi SPAS-12 shotgun is TRAT Special Forces team leader Lieutenant Dylan Morton's weapon of choice.
A Chinese Type 69 RPG is fired at the Tyrannosaur during the base attack by TRAT team member David Fork, distracting it (and destroying its left eye) long enough for Dylan and Regina to avoid becoming the main course.
MP5KN
Shown wielded by Regina in promotional art and usable akimbo style by her in-game are dual MP5KN sub-machine guns loaded with 15-round magazines.
M249 SAW
The M249 SAW appears as the Heavy Machine gun in-game and is a Regina only weapon and features an odd looking thumb hole stock. Two normal M249 SAWs are seen mounted in fore and aft pintle mounts on the Jeep commandeered by Dylan and Regina when they're attacked by two angry Triceratops.
WA2000
The WA2000 appears mocked up as an anti-tank rifle minus a rifle scope and with synthetic furniture instead of a wooden stock and fore grip. It is a Dylan only weapon and is suspected to be of .50 caliber, judging by the size of the spent casings.
M-47 Dragon Anti-Tank Missile
The M47 Dragon Anti-Tank Missile, usually used in a stationary position is mocked up as a portable anti-tank rocket launcher. Used by Dylan and David, it's the most powerful weapon in-game.
The HK69A1 is made up as a Flare gun in-game called the Signal Bullet. It is used during the Allosaur Nest and is used by both Dylan and Regina to signal for an artillery strike.