Knights Armament Airsoft URX3 M4A1 Airsoft AEG - High Speed Edition (Package: Add Battery + Charger)

"This is really good gun It shot over 200ft and was very accurate. The only problem was the threaded barrel. When I tried to put a 14mm negative flash hider it didn't go on then I tried my friends 14mm positive flash hider and it went on perfect

"Fairly accurate out of the box (only tested to 30m, but could easily hit a man-sized target). The externals on the gun are very high quality and extremely solid. The stock and included kac-style iron sights are also good quality and have zero wobble. Threads are 14mm+.

My only (slight) gripe with the externals is that the dust cover can't close, but that doesn't take away functionally from the gun. However, I have seen some cylinders become dented through the mock bolt from an unluckily-placed bb.

There are actually only 13 teeth on the sector gear, and 12 teeth on the piston (2nd tooth removed). However, the piston is polymer with a metal release tooth. I was getting around 14rps on a 2000mAH 25C 7.4V LiPo that fit in the buffer tube, and the gun was shooting ~315fps on 0.28g bbs (~1.28J). Hopup unit is not rotary unfortunately.

My only functional gripe about the internals is that the included M170 motor is WAY too strong for the energy of this gun. I had to replace the motor to something more tame because both the stock wiring and the wiring for the Gate Aster I installed were getting way too hot with the stock motor in.

Something that should be noted is that the gearbox doesn't necessarily play nice with other piston heads unless the piston is short-stroked by at least 1 tooth, as the metal behind the piston is thicker than in other gearboxes. This can cause the piston head to get slightly stuck when its pulled back, which will delay the release and can cause teeth to strip, as well as overheating of the motor/wiring.

Very specific side note, but Perun V2 hybrids don't necessarily agree with the shape of this gearbox, as the trigger magnet physically hits the vertical sensor, which is a no-no according to Perun's manual (I'm not sure exactly what part of the gearbox causes this misalignment). This was tested using G&P, CYMA, Retro Arms, and Krytac triggers with the Perun unit in various positions.

Overall 4/5 for nice externals and pretty decent oob performance, -1 star for non-apparent piston head compatibility issues and overpowered motor.