My buddy is crazy into it. He goes here:
http://www.trinityairsoft.com
My buddy says that he really looked and this site is the only one he found with accurate, definitive specifications- whether the gun is co2, green gas, electric, or pump, which parts are metal, the power of the gun (FPS) etc.
He also says its easy to find guns on trinity and then copy + paste the model number into a google search if you don't like the price.
A few things I've found, doing the airsoft thing with him. I feel I need to pass on my experience.
1) DON'T BUY GREEN GAS. All of the other kinds of gun are plenty safe to shoot AT people, i've been shot in the throat by a co2 pistol at nearly point blank, maybe 5 yards, and all I had to show of it is a welt and some momentary cursing. However, Green Gas is dangerous. Its too powerful to shoot at people, even with adequate airsoft protection its just not a good idea. It can injure you in the way a BB gun can. People usually target practice with them etc.
If your unsure its safe, don't do it. Better safe than sorry. Although, weve had co2 guns we basically shot at someones arm with as far away as seemed safe, and were glad to find its relatively ok. I do reccomend you try it on yourself before you shoot your son with it... kids aren't always as stoic. Also you'll find it stings more when its surprising or your standing still, while getting shot while playing a game or running or whatever it seems to hurt a lot less. This is because of the focus you have on what you are doing, adrenaline, and the fact that you are "Expecting" but not "Waiting" to get shot at some point. It really does work like that. And never shoot yourself or anyone at point blank, that is, if it is less than a yard from your skin or someone elses, it can draw blood. Its not gonna permanently injure someone but its not a real good idea. I had a friend who thought he was cool and took my co2 pistol, put it against his arm and pulled the trigger... he had a bleeding hole in his arm, about the size of a bb. It fell out, but he was nonetheless bleeding, not good, ya'know? It also seems feasible he could have lost the bb in his arm.
2) Usually guns that are fully automatic are electric, in fact I've never seen an exception. Not all electric guns are created equal, and the price tag is more relative than it seems. I have a $100 gun from Walmart, its accurate to a few inches off the target, has a removable stock, shoulder strap, and flashlight lugs, fires consistently, jams little, has a decent ROF and decent FPS. I haven't needed to upgrade yet. However, Its white translucent plastic and honestly looks like crap. However, aforementioned buddy of mine bought a really nice AK-47 replica, that is primarily metal and of a more accurate size and feel, but it skips bb's every third round, has similar fps and worse rof, jams way too much and is fairly innacurate. That said, a friend dropped mine on the stairs and broke the stock, while my airsoft buddy barely jarred his AK and had the battery cavity break. Metal doesn't always mean better, although it certainly can. It really matters WHERE the metal is, and the quality of its design.
Where the specs are important is in the clip and the mechanism that works it. Typically, guns that have huge ammo capacity suck. You want a clip that feeds a single line of bb's into the gun, not something that you have to shake them into the mechanism etc. It will also assist you with stealth.
FPS is also important, but too much is unnecessary. 350 is good, 400 is plenty. Any more will just hurt people.
3) My advice is to go to a real brick and mortar airsoft store. Better than buying a gun that looks like it works good, then find out it doesn't. I've been there, I bought a gun that looked very similar to a lasgun from 40k, I had a Cadian Helmet, football pad flak armor and fatigues. It was pretty cool, but the gun was horrible and got replaced pretty quick, as I got more into it. My walmart special surprised me and everyone else by performing so much better.
There are cheaper guns that are effective, but you have to look. It might require buying a few on some kind of return policy, to see what I mean and find a half decent one.
4) DON'T REMOVE OR SPRAY OVER THE ORANGE TIP. I shouldn't need to say this, but thats how cops know its a toy. People have held up banks with airsoft guns, if a police officer sees you pointing a gun at someones head and it has no orange tip, you can get shot, actually shot as in by a real bullet. Its also typically safer to do this in the countryside somewhere, perhaps in an abandoned building or a forest etc. i prefer thick forests personaly. There are also places that are quite literally made for airsoft or paintball, made by the city like a skate park, or rented out to people etc. Doing it in a developed area is just asking for some elderly person to call the police, or actually scaring somebody. That said, I live in a small town and have typically recieved a degree of tolerance. Its treated with tolerance but control, in the way a bank or library would stick signs on their stairs that say NO SKATEBOARDS.
Btw, all references to bb I make, I actually mean "airsoft pellet". They are plastic and a good deal safer. Quality pellets can help your accuracy too, you want moderately heavy ones because they don't get blown around, but two heavy and they drop your range. Also, real BB's are metal and while they are very close in size, airsoft guns are designed to jam when you stick bbs in, for safety reasons... you shouldn't do this anyway.
Hope that helps.
-Zack