Here, I'd like to introduce you to a close personal friend of mine. M41A 10mm pulse rifle, over and under with a 30mm pump action grenade launcher.
Feel the weight.
Corporal Dwayne Hicks
The M41A Pulse Rifle is the standard weapon employed by the US Colonial Marines. It is a pulse action 10mm assault rifle, complemented by a PN 30mm pump action grenade launcher. The two are arranged in an over and under configuration, measuring 69.5cm in length (or 84cm with the stock extended).
The rifle accepts US M309 10x24mm caseless rounds (fed from high capacity 99 round clips) and up to four M40 high explosive fragmentation rounds, which are manually loaded into the internal magazine. The weapon is powered by a lithium battery which is capable of approximately 10000 rounds.
In its primary mode of fire, the M41A unleashes M309 rounds at 900rpm, with a muzzle velocity of 840m/s. A trained operator can unload the weapoon of M40 rounds in under two seconds. The weapon has a maximum range of over 2000m, though it is most effective at ranges up to 500m.
quote from "Aliens", raw values and other data obtained from http://www.alien-resurrection.com