The killed guard had an AK-47 which after he was killed was used by one of the terrorists to kill all the scientists. What is an AK-47? well this is what I found out:
Image from: Olive-Drab.com
The AK-47, also called Kalashnikov, is the standard riffle of the Soviet Army and many other countries in the world. It has been the weapon of choice of the Soviet Army since it entered into service in 1951.
The AK-47 is designed based on the assault riffle principle. During the Second World War the German Army discovered that most modern combat situation happen at a short range (less than 300 meters) and a regular riffle or machine gun, which used a long range powerful cartridge, was usually too much for the situation (too heavy, too cumbersome, or too big).
The German army came up with a design called the Sturmgewehr 44 (STG44) a compact lightweight and easy to handle riffle that uses a smaller less powerful cartridge then a regular riffle. Because the STG44 is a smaller and lighter riffle, and the bullets used are less powerful the weapon is easier to handle and more accurate in close combat.The Russian army liked the idea of the assault riffle and after WWII asked their weapon designers to come up with an assault riffle. One of these designers was Mikhail Kalashnikov and he took designs from other riffles and used it to come up with the AK-47.
The AK-47 uses gas to cycle the next round into the chamber. When a round is fired the gas build-up behind the bullet is redirected back to the chambering mechanism and the next round will be chambered into the breach (as shown in the animation below). Using the fully automatic setting the rate of fire is 400 rounds a minute.
The features that made this riffle such a big success are; the easy of use, maintenance, and ease of manufacturing. That is why there are over 100 million riffles made all around the world. Besides the Russian manufacturer IZH several other countries (mostly communists) have build their own versions of the AK-47.