Has anyone ever tried running 2 regulators together?

I guess my thoughts are that once one regulator is put in place, you'd get more bang for your buck looking for other places where inconsistency could creep in. Most of my consistency issues can be found by staring in a mirror. I'm pretty sure I wouldn't be able to tell the difference in my groups between a standard deviation of 4 fps and 0 fps.

Sure, I've done both of those. But, I haven't looked to see if there's any significant difference in the FPS. My reasoning for not filling to max pressure is that I don't like pushing things to their working limitations. I'd rather take it easy and keep everything jiving happily. My reasoning for using the regulator off the bottle is due to me wanting to shoot for extended periods, and therefore, tethered. I fill to 220-230 (depending on rifle) and tether a bit lower ~210-200. 
Tom

Airsupply it all makes sense what you are saying and for example in laboratory gas regulators you can have 2 stage regulators sitting on top of the gas cylinder. Are a lot more expensive. 

However: dont forget you already got 2 regulations going on in a PCP with a regulator, one is the main regulator and the second is the knock open valve.
the knock open valve equalizes power output already (the same way as it is done in an unregulated gun) so there is a range of pressures when the output IS stable. Independently on the bottle pressure. (if not the gun is not setup right)
the plateau can be wide over 20-30 or more % is a plateau or more over the decreasing bottle pressure.

As for the main regulator: all you have to do is select the working setpoint properly so it is balanced. There is no point to have another regulator the knock open valve is the last component and it can cope with a lot inconsistency
A second stage would improve the quality of regulation to 1-2% creep or so, but it is not worth it will give you little benefit, will add more parts to fail instead.

I shoot with a double regulator but for a slightly other reason. All my SCBA tanks are filled up to 300 bar and the max fill pressure of my steyr is 200 bar. I'm using a HUMA-air inline regulator attached to my SCBA tank to decrease the pressure to about 160 bar. In this way I can leave the hose attached and the valve opened during practicing without having to refill every 40 shots. On a regular practicing session I shoot about 200 shots so this makes it a lot easier.

However, I think this is only useful in static situation like shooting from a bench, I don't know if this is easy when walking through the woods and having the hose still attached to a small buddy bottle or something..

Hi again, fellow Ausie.
I agree with all the other replies. This is not scuba diving where you have to reduce pressure from 200-300 bar to atmospheric pressure. I have an unregulated BSA Buccaneer that will get 30 shots with an extreme spread of about 25 fps. With an after market reg. I get about 22 shots with an ES of about 8-10 fps. the regulator flattens the curve but at the bottom, not the top. I could tinker with spring tensions and hammer weight for hundreds of hours and I might get back the shot count but I would still be 20 or so fps down on the stock set up. If I fill to only 200 bar, I will get that 22 shots at an ES of only15 fps with the extra 20-30 fps. So in some guns, even one reg is one too many.
That's my two bob
Ian

I only get 1.88% pellet velocity variation across 42 shots of 40 FPE on my 25 caliber Marauder. It has a single Huma regulator (set to 1800 PSI). Any end-to-end variation of 2 percent or less, is trivial for most shooting. For me, there is no need for a second regulator.

Hey, Michael
I use an inline external reg for both my guns and it works a treat from the bench. You get most of the pros and none of the cons of an internal unit. The main cons are the reg itself takes up air space and the small volume of the plenum does not replenish fast enough to make maximum velocity. There is also a small variation in that refilling speed between a full charge and the of reg pressure. All this, of course, is irrelevant for hunting.
Cheers
Ian