My v2 kythera has a maximum output of 2.6j on 0.45g bbs, faceless sniper aeg bucking, maxx me pro, 430mm da vinci 6.01 steel barrel at around 200psi. Exact psi is unknown, because the ugs has no pressure gauge.
I found the standard spring that pushes the hop up unit against the gearbox is way to weak. Atm i use 2 springs and 1 o-ring to keep the hu in its position.
Does anyone know a better way to keep it in position?
The system sounds overvolumed using 0.45g bbs, so i assume heavier bbs or a longer barrel may help you reach higher joules.
You can stack O-rings on the barrel and completely replace the spring, and it gives a very very solid lockup.
You also may be able to sand or file the front of the gearbox to slide the chamber back even further, but there is no returning from that, and you can't get away with too much as your mags still have to plug into the bottom to feed. You probably have a good bit of room though, so if nothing else works you could try that.