For a spring upgrade you will need, at minimum:
- T-10 Torx
- Phillips Screwdriver, #2 head
- White lithium grease, not the spray kind
- Radio Shack "Lube Gel"
- New bushings
- New shims
- New spring
It's not too hard to do, I've gotten taking down my G36 mechbox to about 4 minutes from lots of practice. :) The first time I cracked open my TM it took me 5 hours, though, so block out plenty of time.
There's tons of visual upgrade docs online. Check AirsoftPlayers, they've got the ones I use.
Keep in mind that upgraded AEGs will always fail much more quickly than stock. And failures can be stunning: ground gears, cracked pistons, broken motor pinions, etc.
I highly recommend doing it yourself. Not only is it a good thing to learn to how to go something, but in the much more likely event of a failure you'll be able to diagnose and (hopefully) fix it easily.
The Systema M120 is about the maximum field limit at 400FPS +-10 or so. Be careful, this will open people up at point blank ranges, you shouldn't skirmish with it in a close space, like, say, the castle or the town. I recommend the PDI 150% spring. It's easier to work with than the Systema, slightly lighter at 360-375ish, and easier on those close contacts. I use it in my long guns.
