The following weapons were used in the movie Aliens:
M41A Pulse Rifle
The Marines of the USCMC (United States Colonial Marine Corps) famously use the M41A Pulse Rifle as their standard issue weapon, a futuristic assault rifle with a magazine capacity of 99 rounds of armor piercing ammunition with a pump action 30mm grenade launcher underneath the barrel. This weapon was made from a M1 Thompson submachine gun with a Remington 870 shotgun underneath with the shroud and foregrip of a SPAS 12 covering it. At the end of the film, Ripley (Sigourney Weaver) tapes one of these rifles to an M240 Flamethrower when going to rescue Newt (Carrie Henn).
The movie prop was only designed to fire blanks from the .45 ACP Thompson Submachinegun (20 rounds) and Remington 870 Shotgun. The prop did not have to survive the recoil form real 12 gauge rounds being fired.
M56 Smart Gun
Both PFC J. Vasquez (Jenette Goldstein), and Private M. Drake (Mark Rolston) use M56 Smart Guns. These were made from German MG42 machine guns. The body-mounting apparatus was made from Steadicam "arms," with other miscellaneous parts coming from various motorcycles.
Another weapon used by the Marines is the M240 Flamethrower, it most notably used by Gunnery Sergeant A. Apone (Al Matthews), Private M. Drake (Mark Rolston), and Ripley (Sigourney Weaver) when she famously tapes it to an M41A Pulse Rifle before she goes to rescue Newt (Carrie Henn). These flamethrowers also appear to have been created from parts from M16 rifles with the M203 handguard. The 'faux' flamethrower used the upper receiver assembly of an M16A1 - cut into two parts, using the top handle facing forward, but the section with the ejection port turned backwards.
Corporal Hicks' (Michael Biehn) shotgun is an Ithaca 37 "Stakeout" which he keeps for "Close Encounters". One memorable scene with this gun is when Hicks sticks the barrel of the weapon in an aliens' mouth, and yells "Eat This!" and proceeds to blow its head off. In the process the acidic blood gets sprayed on to Pvt. Hudson's (Bill Paxton) arm because he was trying to close the door of the APC.
The Heckler & Koch VP70 is the service pistol of the Marines in the movie. This gun is notably seen in the hands of Private Frost (Ricco Ross) just before the aliens attack. Cpl. Ferro (Colette Hiller) attempts to draw hers from its holster, but is unable to in time when an alien gets aboard her ship. Lieutenant Gorman (William Hope) uses one to shoot at aliens during the airshaft scene.
Trivia Note: In the special features included with the Collector's Edition DVD, it is mentioned by one of the film's armorers that the VP-70 was chosen as the standard issue sidearm for the Colonial Marines because of its "futuristic look" as well as its relative obscurity; it is also is no longer manufactured.
In the extended version of the film, the Marines set up sentry turrets in the hallways leading to their refuge. These were built upon WWII German MG42 machine guns, the same used for the smartguns and provided by Bapty's (movie armorer of the UK). Only the ammo drums on the side are from WW1 German Spandau Maxim LMG 08/15 machine guns
PFC Vasquez (Jenette Goldstein) uses a blued Smith & Wesson Model 39 with Ivory grips as her sidearm. She most notably uses it to kill an alien while moving through the vents, but burns her foot from the creature's acidic blood in the process.
