Quinn Abercromby (Christian Bale) keeps an Ulriks Mauser Tyrannosaurus Rex or T-Rex rifle in the massive .577 Nitro cartridge and is seen with it several times in the film, most notabley when he faces the Male Bull Dragon and fires at it. Like the .600 Nitro double rifle in The Lost World: Jurassic Park, this gun is an expensive, rare gun customly crafted by expert gunsmiths. The gun is said to have such vicious recoil and overkilling firepower, even hunters in Africa only keep it as a back-up gun incase of a charging animal. Even with such immense firepower, the rifle mananages to do little more than make the dragon mad. When looking closely at the front sight, it appears they used more than one rifle in the film as the front sight changes in some shots.
Denton Van Zan (Matthew McConaughey) uses a pistol gripped Mossberg 500 with a super-short barrel and a finger-grooved foregrip on the pump as his main weapon throughout the film, keeping it slung at his hip like an over-sized sidearm.
While bows aren't usually considered firearms, bows with Magnesium Phosphate C4 arrow tips are a different story. Van Zan and Quinn both use these crossbows when facing the Bull Dragon at the film's climax. Van Zan tells Quinn that the only way to kill it is to wait when it breaths fire, because only then does it expose its chest. Van Zan almost hits the Bull while standing on a tower, but it breaths fire and the arrow only manages to ignite its flame early, damaging its mouth and causing it to breath smoke. When Quinn faces it, he loses his arrows whilst doing a Judo roll away from the dragon as it strikes. He manages to grab one of the arrows and right before the Bull torches him, he fires it into the dragons mouth, blowing up its napalm valve and severing its head.
When killing the first dragon, Van Zan mans a large vehicle mounted Harpoon Gun and fires it just as the dragon flies over the hill, killing it with a harpoon to the chest.
