I actually find Marui Version 7s the easiest. The electronics are all external and once they are removed, all you are left with is the mechanics of the mechbox only. The Tappet Plate spring can be installed after the case halves have been assembled as well. The only real time consuming part is accessing the mechbox for the M14.

+1

Very easy gearbox to work whit for a first timer. Just remember to take the time to take picture or draw diagrams of how things are places before removing them.

Another tips. find a magnet and stick every scrw and spring on it, that way you wont loose any. Migth seem dumb, but it can really ruin an upgrade experience to spend an hour on your knew looking for that small f++king screw.

I wasn't really planning on doing it my self... lol I have someone I trust with my guns (The only person I really trust) I was gona ask him to do it. After watching him do it once I'll know what I'm doing and be able to do it later.

This is what I did to my TM M14 OD:

Guarder standard steel gears
Guarder steel cutoff lever
Guarder metal bearing spring guide
Guarder polycarb piston head (non bearing)
G&P polyacetal piston (white)
Systema piston O ring
Systema M120S spring
Systema metal bushings
Systema shims
Prometheus 6.03 x 500 mm barrel
Homemade 9/16" x 5/16" 12g piston weight
Extreme-Fire SW-S MOSFET switch
20A fuse upgrade
King Arms bolt release
G&P scope mount
UTG/Leapers 3-9x50 red/green illuminated reticle scope
Guarder M1907 type black leather sling
Every thing else is stock TM

It's muzzle velocity is 385fps with a .25g BB and 420fps with a .20g BB.

It rate of fire is 17bps with an 8.4v, 3300mah sub c large NiMh battery and 19bps with a 9.6v, 1700mah 4/5 sub c NiCad battery.

It can hit a man sized target, 9 hits out of 10 shots at 225 feet.

To date, I have 16,000 rounds through the gun.

I'm in the process of converting it to a sniper rifle. I'd like it to shoot at least 550 w/ .20g BB.
I'm putting in:

Madbull M150 spring
Guarder infinite torque motor
Prometheus double torque gears
Prometheus hard bucking (red)

My TM M14:
http://img519.imageshack.us/img519/5...2102403jw7.jpg

Whats the difference between M120S and M120 spring?
Whats a mosfet do lol

An M120S is a stainless steel version of Systema's M120 spring. It's supposed to be slightly harder.

A MOSFET is a Metal Oxide Semiconductor Field Effect Transistor. In an AEG, it gets wired between the battery and the trigger switch contacts. Instead of the current from the battery to the motor going through the trigger switch contacts, the current goes from the battery, through the MOSFET to the motor. The trigger switch uses a small current to turn the MOSFET on and off when you shoot your gun. It eliminates the arcing and wear on the trigger switch contacts making the electrical circuit much more reliable. It also generally gives a shorter physical path from the battery to the motor, increasing the electrical efficiency of your AEG.

For more info, see:
http://extreme-fire.com/

So a mosfet is a good investment?

Yes.

See:
http://extreme-fire.com/
I use their SW-S:
http://extreme-fire.com/SW-S.html