Gearbox's are the main part to a airsoft gun, well an AEG i could spend hours explaining all of how each gearbox works, version 2 and onward theres alot, but im going to let one of my more favorite youtube people do so, airsoftgi a airsoft store who also keeps open and know with there youtube!, i order from them, theres also evike, airsoft megastore, airsoft california, blahblahblah you get the drift? but below is the video it shows all you need to know about AEG's i give all the credit towards Airsoftgi.com

<iframe width="560" height="315" src="http://www.youtube.com/embed/zoyoFaC6XRA" frameborder="0" allowfullscreen></iframe>

Airsoft is lots of fun from little kids just beginning, with cheap springers, who will later evolve to actual "airsofters" with the expensive good equipment, and play at a much more "hardcore" level like perhaps in a "op" operation, where large amounts of serious airsofters play against each other, in teams with even realistic war settings like "mil sim" military simulation, where alot of the facts and how the game is played is like real war. but heres just a quick link to a cool video from one of the indoor fields i play at in Fallriver
link- http://www.youtube.com/watch?v=HS0VtIBdxmQ&context=C3ee3182ADOEgsToPDskKknjhm04FRZ7fbRLtOddWY

Now a huge controversy in airsoft, AEG or GBB some prefer the realism of GBB, but others like the cheaper *in most cases*  but trustworthy AEG, what is your prefrence, mine has to go to AEG as well its simple to keep clean and running, and works like a charm, GBB are still a little "misty" to me... see what i did there? HAHAHAHA, but back to the subject, i dont have a true full understanding of GBB rifles and pistols, i have used some and truly enjoy the realism with the nice kick they deliver!, but for rifles i will always be AEG

An AEG Gearbox- the main mechanic that runs an AEG *besides the motor* *P.S this is a  version 2 gearbox which is very common in M4 *setting base as M4 as its most common* Variant rifles
Link- http://i60.photobucket.com/albums/h24/ajpadre/CA_M15A4_CQB_Gearbox.jpg

Airsoft is a new innovative sport, A military simulation game using AEG's *all electric guns* to GBB *gas blow back*, ill go into detail about those later, but first, airsoft gives you a rifle, pistol, etc, that fires a 6mm plastic BB, this game runs on something known as the honor system, when you are hit by said BB you call a "hit" and either you go back to spawn, or a medic can bring you back in! depending on the rules, theres many "gamemodes" playable, CTF *capture the flag* team deathmatch, and well pretty much any generic gamemode from FPS's *first person shooters* you can think of! this game can get people un interested in boring sports like football, etc and go for action packed tactical gun em down fun! From realistic "operations" where facts and how you play are like real military tactics, or just regular play with friends, or people a field and gun some people down! Now to go into a gun how it works, AEG's run on something called a gearbox, when a piston is pulled back by gears inside the gearbox then released it then pushes the pistion head and pushes air into the air nozzle creating high power push from the air pushing the bb out of the hop up *a small device ment to spin the BB* then out the barrel! i do not know much about GBB i soon shall get a GBB pistol then disassemble etc, and learn the internals and post it! If you have any questions please ask, if i forgot anything post it and i will update!

                          Link- http://ncs.sc/times/wp-content/uploads/2011/03/cat-airsoft.jpg