Classic Army M134 Minigun HPA

[rotazd]

I'm having serious issues with this shooting, bb's are shooting no further than five/ten meters and FPS seems to be very low..even at maximum of 120psi going through the air hose. There doesn't seem to be any obvious air leak, hop adjustment hasn't changed a thing, switching out to a bigger battery hasn't made a difference (other than the barrel spins faster). I'm absolutly stumped, help anyone!?
Using Wolverine Storm reg, 12v battery or 14.4 lipo battery.