So M140 is more than enough ?

Didn't you read what the guy just above said? His 400fps gun uses a M110.

Tuning and optimizing your air system is more efficient than putting a big spring in a gun that loses efficiency everywhere.

i think the problem here is the OP thinks that hiting 450fps is going to give him a range advantage over the rest of the guns running 400. lets just put it out there for him that fps doesnt really have a huge effect on range. Fps will allow u to use a heavier bb effectively, a heavier bb will carry energy out to a further range, but if yer hop up camt provide enough lift for the heavy bb its useless to you. Between 350-450 fps you will get about the se effective range but with a 350fps gun youll he using .25-.28g bbs, with 400 .28-.32 and with 450 .30-.36 (if yer hop can lift a .36) a well tuned 400fps gun can prety near range my 500fps bolt action. Runinng 450fps now yer hit with a minimum engagement distance (probably 100feet or so depending.on host/field rules) suddenly you need a good sidearm for engagements within 100feet, keeping in mind that im most cases airsoft engagements are goining to be in the 50-150foot range. I personally would shoot for the 400fps mark (as alot of fields arent going to let u run 450 on an aeg, most guys who do are guys who are certified snipers trusted to play safely with a high powered gun, epecially.one that is capeable of a high volume of fire) hit
400 fps, nice and consistant, good inner, good hop up, good bb's and a low zoom optic (1.5x or 3x or variable starting at one of those) dial it all in and you should be able to reach out beyond the range of most other guns on the field, unless there are a bunch of ptw's in yer area then just get certified and build a bolt action if u want range on those lol

So what parts would you recommend? Have you seen the previous post I made for the parts? Thanks in advance ! I just want a more accurate gun than can hit 200+feet.

prometheus smooth hop rubber and bridge tenssioner (orbthe modify flat hop)
a good barrel, lotta choices. Madbull, prometheus lots in between, get something good that you can afford.
good piston (lonex makes a nice one) shave off the seccond tooth(the one after the pick up tooth)
good piston head (lots to choose from)
sorbo pad.
if u want u can do a fet (like the merf 3.2) while yer in there to improve trigger response and support an 11.1 lipo.
Thats about it, the stock spring in that gun should alrdy be over 400 fps from what ive read its 420ish and youll prolly go up a bit by improving the piston head.
you could also do the cylinder head and.nozzle too if.ya wanted to.
and you could do gears as well, maybe go 16:1 for even better trigger response.

All good suggestions, except the piston is NOT STANDARD. You need one made specifically for the SR25/L85/PSG-1.

The alternative is using a spacer that is sold to be put between the piston and piston head. You have to change your gears to standard V2 at the same time.

my bad, i thought the gng was the one with the long hop up and long nozzle. Thats why im going echo1, the gearbox is a lil longer at the front, rest of the parts are standard v2 afaik

edit: evike says standard m4 piston (guessing they mean v2 lol)
Gearbox:*G&G Gr25 series uses regular M4 type piston. Not the long type.
http://www.evike.com/products/28222/
not that i have huge faith in evike, best bet would be to count the teeth before buyin a piston

I hit mine with a tightbore, helical hi-torque gears, flathop and a lonex gearbox/bore-up kit. Yes, I loaded an M140 into it and the thing was firing 525fps (+/-1).

Bear in mind, I built this stupid thing as a demonstration of how broken the fps rules in my club were (they've since been adjusted down) but I lost sight of the BB (.30g) before it started dropping. I readjusted it to 412fps and it performs just as well.

All in all, it was an EXPENSIVE build (parts worth more than the gun). If you're going for higher velocity, you're paying out the ass to stabilize that projectile.

and was it a standard v2 piston or the long one?

Standard. It's a V2 mechbox with a retard long air nozzle and hopup unit.

Sorry to ask a potentially dumb question
 

So would a M120 or M130 work? Without replacing anything else?

No. Up your inner barrel to a tightbore and put on a better hopup bucking/nub.

You add extra velocity and you need to do more work to stabilize the projectile and that means better airseal and clean barrel.

As an owner I agree with Janus. The stock gun is fairly good. A nice barrel is really the only thing it *needs*. Stock motor is sort of weak-sauce. For a while, I ran a simple fet and a HUGE (like 50C) battery and lonex motor to get some super snappy trigger response. Then I got a chimera and could dial it back to a regular lipo. You really don't need a heavy spring. Focus on your airseal and barrel group for now.

Cheers