This is my first gun review, so please bear with me.
The A&K M4 S-System is one of the many recent AEG clones out of China. However, it's quality is better than most MPEGs, even to the level that I'd call it an AEG. I bought mine from
Airsoft GI with an M100 and steel bushings upgrade. Here goes-
A&K M4 S-System AEG
First impressions:Heavy! Since all the RIS (and some other parts) is metal, the gun is pretty heavy. I also noticed that the handguard is pretty big, a lot bigger than a normal M4's. I was very impressed looking and holding it for the first time.
The box it came in-

Inside the box-

It came with the gun (of course), manual (rather detailed, with decent English), some paper targets, small screwdriver, un-jamming rod, a metal midcap magazine, a battery, charger, nice speedloader, a little baggy of actually good bbs, front sling mount, and front sight adjustment tool.
Appearance:This gun looks great, the plastic is good and the metal isn't crappy. If you were to put this gun next to the Tokyo Marui version, I honestly believe that you'd have to look twice to distinguish one from the other. That's about it, I can't say anything bad about the looks. Some people don't like the "fake" trades, or find them annoying; they don't bother me at all. I'd rather have fake trademarks that are there, than have realistic trademarks that have been burned/scratched off...
Here's a picture of the trades-

Left side, sights down, stock in-

Right side, sights up, stock out-
Feel:The gun feels very good and solid. The weight of the A&K is probably very close to that of the real thing. The plastic feels smooth and sturdy.
Build quality:This is a well built gun, especially for the price. As earlier stated, the plastic and metal aren't cheesy, and they're sturdy. The only weak thing I can see on the gun is the forward assist knob, which could pop out someday (but could probably be put back in, and isn't a big deal). The other thing is that the upper RIS pin keeps sliding out, so I just took it off and put it somewhere safe. This hasn't seemed to affect anything, as the RIS is screwed in securely in several places. The whole RIS system is metal, and so is the outer barrel. Other metal parts include: sights, mag release button, dust cover, charging handle, sling mounts, trigger, selector switch, s-buffer, and screws. For the price, a very well built gun.
**Update** Yesterday, ~1 month after buying the M4, I leaned my gun down against a dresser while I got something in my room, and it fell- resulting in the upper receiver tabs breaking off. The impact shouldn't have been too hard, and it was on carpet, but from what I'm hearing this seems to be a common problem with the A&K M4-S. Here's a picture, the plastic tabs snapped off-

Here's a link that might help if this happens (I roughly followed it to fix my M4), even though it's in Japanese-
http://www.interq.or.jp/tokyo/akishino/factory/M4%20Frame%20Lock%20Pin%20Restoration/Lock%20Pin%20Restoration.htmFunction:The gun fires well, which I'll get into on the next section. The sights are fully adjustable for perfect accuracy, and fold up and down well. The battery fits in the handguard very well (and much better than my last MPEG- a UTG MP5...), and changing the battery out is quick and painless. Like the real thing, this gun has many moving parts. Moving parts (besides the obvious ones) include the folding sights, charging handle, forward assist knob, dust cover, and trigger guard. The charging handle is smooth to pull back and gives a resounding clank when let go of (and when the dust cover flies open). All the moving parts work well.
Performance:I don't have a chronograph, so I can't say exactly what it's fps is (although it wouldn't matter much because I have a M100 in it). The range and power of the gun are very good. I can easily hit a man-sized target at ~120 feet, this is greatly influenced by the stock tightbore barrel. It has adjustable hopup, like most guns these days, located under the dust cover-

The gun's performance is rather impressive for only having an 1100 mAh 8.4V battery. It's pretty loud and high pitched when it fires, not sure if that's good, bad, or means nothing. So far, the gun has performed well, with few misfeeds or double feeds.
Accessories:As this gun is full of RIS, it's external add-ons are nearly limitless. The gun's stock can be exchanged for a full or crane stock, if desired. The compensator will screw off, allowing for mock silencers or other compensators to be added to the weapon. A kind of neat thing is that you can still use the iron sights if you have a big enough (30 or 40mm) red dot scope on. Basic upgrades include: a sling, RIS flashlight, RIS laser, bigger battery, foregrip, and a variety of scopes. Personally I bought 4 Star magazines, a foregrip, and Leapers Red/Green dot scope. I highly recommend getting a foregrip because of this gun's weight, and it also makes general manuevering of the weapon easier.
Conclusion:This is a very good AEG clone coming out of China, well built and sturdy. It's very customizable as far as the RIS and accessories to put on the rails. I highly recommend this gun to any beginner wanting an MPEG, or also to experienced players such as myself that are looking for a good gun at a decent price.
Pros- Great price
- Well built
- Lots of RIS
- Tightbore comes stock
- Ni-MH battery (no memory)
- Great MPEG
Cons- Heavy
- A few loose/brittle parts
- Small battery (but you can buy a bigger one)
