Ok, the Boyi, or D-Boys, M4 is an AEG. An AEG is an Automatic Electric Gun. This not a real gun, it is an airsoft gun. Airsoft guns shoot small plastic BBs that have different weights and are 6mm in diameter.

The gun I got was a 2007 version which I hear is better than the older Boyi models so there may be differences.

Contents
In the package is the gun, one clip, a detachable foregrip, a shoulder strap, a battery pack and a charger.

Gun Build
This gun claims to be full metal which is a little bit of a lie. The outer body is metal with the exception of the foregrip attachment, the main grip, and the stock which are all a high quality and duarable plastic. The heart of the gun is it's gearbox and thankfully this gun is equipped with a metal gearbox. In short, having a metal gearbox enables you to internally upgrade the gun further down the line. The stock on this gun is extendable with many different lengths that it can be stopped at. This gun is also equipped with a hop-up system which allows you to change the spin on the BB thus directing its flight path. You had better have some muscle on you to use this gun, it is heavy. I believe it to be upwards of 7 pounds which gets tiring after lugging it around in a forest for hours.

Quality of Firing
The Boyi M4 that I got is rated at 330-360fps. This means that the BBs are travelling at 330-360 feet per second when they leave the barrel of the gun. This claim seems to be pretty accurate because it hurts to be shot by this guy. Once the sights are dialed in and you've adjusted the hop-up to your liking, this is an accurate gun when used up to 100 yards. It is a dead ringer below 30 yards and still packs quite a punch. There are three settings of fire: safe, semi, and auto. As expected, safe makes it so the gun won't fire, semi shoots one shot with each trigger pull, and auto shoots at about 25 shots a second with a likeable spread pattern. Seeing as how the clip holds 300 rounds, even on auto it takes a while to run out of ammo.

Battery and Charger
The battery that came with it is a good battery that lasts a good 10 hours or so of moderate firing. It fits into the stock kind of oddly but it works. The charger is kinda lame but it still works. It is just a plain old wall charger that takes a long time to charge. If you want, there are quick chargers available that work wonders. They charge the battery in about an hour and stop when they're supposed to.

Upgradeability
The M4 has a metal gearbox which allows the internals of the gun to be changed out for more powerful counterparts. These could include a new spring, pistons, gearbox, barrel, etc. If this is the route you choose then there are many good websites dealing with how to upgrade the internals. An easier upgrade would be one of many external upgrades. This gun utilizes a full rail system like a real gun so many things can be attached. You could take the ironsight off and replace it with a red dot sight like me, or add a rifle scope. The foregrip can easily come off and be replaced with a replica M203 grenade launcer that uses CO2 power to launch grenades filled with airsoft BBs.

My Reccommendations
-Use only high quality .2gram BBs that have been triple polished to avoid damaging the hop-up system. Cheap BBs from WalMart have seems that will tear up the rubber used for hop-up. This will make the BBs path unpredictable. Killer-Bees is a good brand.
-Don't upgrade until something breaks. Yes, something will break, it's just a matter of time. This is a mechanical device just like your car. To prevent premature breakage, learn to take apart and clean your gun.
-Before putting the gun away for the day, dry fire a few times on semi-auto. This puts the piston back to its farthest position which extends its life.

Recommended: Yes