Downgrading of GBB Pistols?

bullets

Can you downgrade a GBB Pistol?

I want ot buy something like this:
(There seems to be different versions)
http://www.redwolfairsoft.com/redwolf/airsoft/ProductDetail?prodID=22284
http://shop.ehobbyasia.com/default/pistols-gbb-smgs/western-arms/wa-gbb-infinity-6-0-high-brid-dx.html

Depending on different sites I got I am getting a range of FPS's listed
from 310fps to 345fps. I dont want to risk ordering one until I know I can get
one sub 1j
(and I need to get a store thats in stock and would rather order within Europe and
pay via a store that accepts paypal as My Credit card needs re-newing)

~B

NakedDex

They tend to overestimate the power of gbbs. Especially from our point of view. Gas efficiency is heavily dependant on air temp, humidity and barometric pressure. All of which are very different in HK where these claims are made. The sigificantly lower temp and air densities experienced here on an average day mean you won't get a gbb to run at ~320 on 134a. Green will give you around that figure but, unless it's heavily upgraded, wouldn't push over the limit.