There are several variables that can be at play in this scenario. I don't own a FX, but I get reg creep on my rifle as well. Reg creep can go up OR down in pressure. Reg creep usually occurs before the regulator has settled in to it's set pressure. It may take 50 shots before the reg fully settles in. The reg is not leaking. The way you know the reg isn't leaking is because the pressure loss in the plenum (regulated side) would automatically be compensated by the pressure from the bottle. The belleville washer stack and o-rings are set to a specific level. If you have an air leak on your reg, you'll see the pressure in the bottle drop while the pressure in the reg stays the same. That is until the pressure in the bottle drops below the set pressure of the reg, then both gauges will show identical pressure settings, and simultaneously drop pressure. Are you leaving pressure behind the bottle and the reg while you store the rifle, or are you unscrewing the bottle each time? I've heard that the o-rings in the regulators like to have at least 1000 psi left on them to maintain their seal after the reg settles in. I do realize that FX has bottles that can be taken off at will without having to release the pressure, but I'm not sure if this helps with the issue you're having. Every time you release the pressure from the bottle, and then reapply a full load of pressure, you have to let the reg settle in all over again. And every time you adjust the reg, it needs to settle in.
I also experience reg creep right after filling the bottle from a scuba tank. Even on a slow fill, for some reason the initial fill causes reg creep to go above the set reg pressure. Then after the first shot the reg will settle back in. It's not by much. Maybe 5 or 6 BAR of creep.
Can you be more detailed as to when you see the reg creep? Run us through the scenario or events and time frames when you notice it. I'm sure there are more people on here that have theories and experience with what you're going through.
