Deep Blue Sea
The following weapons were used in the film Deep Blue Sea:
Mossberg 590 Mariner
Carter Blake (Thomas Jane) pulls a Mossberg 590 Mariner shotgun with a pistol grip, Choate folding stock, and high-capacity magazine tube from a case in the aquatic lab during the first attack by one of the sharks. He chambers a round but doesn't get a chance to fire the weapon.
Heckler & Koch P2A1 Flare Pistol
At one point in the film a member of the lab's staff, Brenda Kerns (Aida Turturro) fires off a pair of Heckler & Koch P2A1 Flare Pistols when the staff hold a surprise birthday party for Dr. Susan McCallister (Saffron Burrows). The black powder from the remaining flares is then used to create a makeshift bomb as described below.
A spear gun using the stock and receiver of a Remington 700 rifle is seen being used by Carter at the start of the film to capture an escaped shark from the research facility. It is then used by Sherman "Preacher" Dudley (L.L. Cool J) at the climax of the film to shoot the last of the sharks, the spear having a makeshift bomb made using the black powder from several flare gun cartridges. The steel cable trailing behind the spear is then put to a car battery, the electric current setting off the bomb and killing the shark.
The spears makeshift bomb is constructed from flare gun cartridges. The cartridges are disassembled and the black powder is poured into one of the original spears. The spear has a steel cable attached to it and when it's connected to a car battery the bomb explodes. Carter Blake (Thomas Jane) is seen making the bomb in the movie. This scene was also tested on an episode of Mythbusters.