CYMA Adjustable Full-Size M16 Precision Rifle Stock for M4/M16 Airsoft AEG Rifles
(Color: Black)

"After applying this to my rifle, I feel that I can now leave an honest review.
The stock comes fully fitted eith the stock adapter, and a few details that are not on any actual M16 stocks. For me this was fine.
It came with no guide for disassembly nor application, so I had to find out myself.
To disassemble, first press the button on the right-hand side of the stock. The pull off the first buttplate. Afterwards, unscrew the button by twisting. Remove the spring and insert. From there you can unscrew the screws on the inner buttplate (flathead screwdriver), and extract it.
Now, for Lancer Tactical M4s, you would now have to get an M5-80 85mm (80mm works fine) screw.
To reassemble, first attach the inner buttplate back on the gun. Second, remove the moving lightly-serrated object in the inner buttpad. Slide the insert into the hole and where it once was. Next, you need to add the spring and screw back on the button. Rescrew the screws on the inner buttplate and reinstall lightly-serrated object.. Finally, hold down the button and slide back on outer buttplate.
PERFORMANCE
I used an 80mm screw with proper measurements as it was the only one I could find. The stock itself doesn't wobble, and rests only slightly offset to the gun itself. It also rides a tiny bit of an angle, but most people won't notice it (probably because I used an 80mm), but it doesn't impact cheekweld at all. It also tapers a tiny bit smaller than the tang of the lower receiver by the grip.
The stock is big, and there is no noise besides the batteries clunking around in the hollowed-out stock.
It is about the same weight as an actual M16 stock, so that's a plus.
OVERALL
Overall, the only bad thing about the stock is the lack of documentation on it. Hopefully this review can help your decision on whether to buy or pass this stock. Good luck airsofting!

"Material is pretty solid and good quality, Install is also pretty simple, and the fact that the rear pad is adjustable I think it's quite nice, reason I can't give it 5 stars is because if your gun is rear wired, it'll be a pain in the butt to grab the cable to plug in your battery due to the adjusting mechanism of the rear pad, other than that it's a pretty nice stock!