Hej Carl,
Selvom du er dansk, så tager vi den på engelsk;-)
Great to see a fellow Dane here so had to great him in our local tongue
And great to see some love for the Dark Side in a place where people are still mostly shooting band guns and even in the shops they'll tell you old tales of how much maintenance a pneumatic gun needs. Sorry for the rant, I just find it plain silly.
Anyways, back to Carl.
I reckon your One Air is assembled with its handle and therein lies the problem. Take the handle off by punching out the retaining pin just about where it meets the barrel. It's a tight fight. You'll have to find something of more or less the same diameter and maybe even take a hammer to it.
Once the handle is off you can screw in the pump. Pump it up to about 18-20 bar to start with until you get used to loading it. Later on, you can always put more in. I have 23 bar in my 120 but that's more for open water and I suspect you'll be hunting the shallows around rocks a lot.
If you have the pressure gauge, then good. If not, then there should be a table of pump strokes and resulting pressure in the manual.
Once pumped, fit the handle again and go spear. Remember to always flip out the line release before you load the spear and cock it.
That's pretty much all there is too it. You might find a one or two things annoying - though you should love the gun for its fast and powerful shots.
Eg. when it is not loaded, there is no where to put the spear. Put a rubber band around the muzzle and one on the handle to hold the spear. That helps a lot. Likewise, when you have to exit the water, you have to shoot to unload, but that's a minor nuisance.
Just be aware that 80 is likely the size where the tip of the spear will be by your face when you are almost loaded, so tilt the gun away from your face when you load it. Just in case you make a slip and the spear gets away from you before you have locked it in the trigger mech...
Let us know how you like the gun.
I suspect it will be a great gun for mullets and trouts though it may not track as fast as smaller barreled bandguns.
I'd love to see more praise for pneumatics in DK