Anyone had any reg creep on fx maverick or m3

There are many guns out there with 300 bar fill and only 1 reg. You do know that right? So not sure why you doubt the first reg will handle 300 bar on a $2000 gun. Even a cheap $300 average pcp is fill to 300 bar and have a single reg with no problem. 

It doesnt matter how much the 1st reg is subject to. It will regulate that pressure down before going into the 2nd reg. It may creep a little due to the higher 300 bar fill, but even that little creep will have no effect on the 2nd reg.

Example, 1st reg is set to 150 bar, fill pressure is 300 bar. The 1st reg might creep to 160 bar. But 150-160 bar going to the 2nd reg will have no effect. The 2nd will regulate that 150-160 bar to say 120 bar.
 
i just installed the dual reg system from huma on mine. to be honest in a day or 2 i will remove it as after seeing what happened to the exploding plenum i got scared and dont want anything external or aftermarket part on my riffle.. the numbers look promising but the huma gauge is off by 15 bar and the regulator was set at 220 bar instead of 135 as was indicated in the bag
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Creep happens to all rifles, cheap and expensive. It is pretty common. It's what keeps HUMA , Atraros and Lane in business.

You can try to replace the inner o-rings, it is a headache but can save a lot of $.
Just to add to this instead of starting a whole new thread. I just got a Maverick and as it sits over night it does creep about 7-8 bar. It takes awhile for this to happen and I notice no ill effects while shooting. It’s kind of an is what it is whith airguns. I notice taking it through varying temperatures increases the speed at which it happens. Air is ever changing in pressure and densities due to changing environmental conditions. Let’s face it, this is a limiting factor for airguns vs powder burners. You will drive yourself absolutely insane in search of a reg that can sit long periods and not change at all. If you do find it having it stay that way for super long may prove challenging. Pcps use a lot of pressure and I’ve never owned one that didn’t creep a bit. Again is what it is.
 
Reg creep on the first reg means absolutely nothing as it has zero affect on the second reg. It may in theory save some wear and tear on the second reg by feeding it a lower pressure. I somewhat doubt the value of that as well.
On my M3 I have the 1st reg basically dialed out of existence. Having to remove the bottle and not being able to actually see what your adjustments have done without putting the bottle back on is a ridiculous design to facilitate what I believe is more of a marketing feature than a functional feature. Note the Panthera is a single reg gun and it seems to be the new flagship gun for them