Marauder fill pressures...

If I could be so bold and suggest you leave it alone and don’t adjust anything. It shoots as good as it gonna get right out of the box. And, the reg is non adjustable. Expect just a little under 900ish depending on shooting altitude with the guns’ preferred JSB 10.34 or the AA’s. I can’t really discern which mine likes better.

Addressing your question...

The only way to truly know it to fill it up just over 2000 psi (no since wasting air to determine reg drop off) and shoot over the chrony until the velocity drops and check your gauge. I marked a spot on the bezel so I’d know when I close to refill. Mine dumps at 1950ish BTW. 

And, the Crosman gauge is no real world pressure indicator. Only for point of reference. Had to replace mine. Crosman (best customer service around) sent one no charge. Neither gauge read the same compared to each other nor the gauge on my Joe B. fill assembly.

Be sure to clean the gunk out of the barrel. 

Happy shooting!

It is my understanding. That’s one of the things you learn. When you chronograph your gun with a particular pellet. 
so just air it up to the manufactures specifications. Take a shot and make notes of air pressure drop. 

The Joy's of a new toy. Putting in the work to figure it all out. Good luck and congrats on the new toy. Enjoy.

@leadfoot

to access the barrel to clean it you can simply unscrew the shroud as a whole while slightly tilting the gun barrel downward and slide it off as a whole. no need to remove the barrel band. You will see a plastic hub with an oring on the outside that centers the shroud on the barrel. you can if you wish, insert a allen wrench or similar tool through one of the holes and "wiggle" it off the barrel. It's simply pressed on the end of the barrel. Not screwed on. 

Medium rings work fine with a 40mm objective but i've always used high to get a better cheek weld and give clearance for the mag. You may have to fiddle with scope location with the medium as the fat part of the bottom of the scope may interfere with the mag location. Sorry, I don't use a mag. I use a single shot tray. I've noticed a much improved accuracy by doing so. Can't explain why; doesn't matter, it just works. 

and to the question about lowering the velocity of the 8.44... 

yes, rotate the hammer spring counter-clockwise. Not sure how much but keep track of what changes you make so you can go back to the original settings. Never was able to get the 8.44's or for that fact any other pellet to quite stack 10 shots like the 10.34. But hey! that's the fun of shooting the gun is trying something new. 

All the best!