The air weapons for my work have been stored all “winter” in their warm, dry cupboard. Only my main tool for accurate work is a pre-charged pneumatic Daystate Harrier.
With the lighter HW35K Weihrauch as my general everything else “springer”.
You should store a pre-charged pneumatic (PCP’s) with pressure in its reservoir.
It’s the only way of keeping the seals intact and prevent them from deforming.
Now I’ve heard some ‘ex-spurts’ fill their PCP’s with clean Nitrogen.
Being chemically inert against a lot of material, it does seem like the ideal storage charge.
It’s also dry air, no trace gases, and bears temperature variations a lot better than mere air.
Only it doesn’t actually impress me as the weapon was designed to use and store AIR under pressure.
Rightly or wrongly I think too dry and too pure a gas could actually harden the material used for making the seals. It would however stop rust from forming within the reservoir.
A good thing you’d be thinking and I agree.
It won’t stop metal fatigue though.
That steel reservoir tube is usually sitting with between 100 and 140 bar in varying temperatures (if you are like me and actually use it in the field). It may fail over time.
It’s the reason why I always cover the rifle when refilling it and fit a double layer Kevlar sleeve round the fore stock in use.
Call it “shrapnel protection” for me as 2500 psi (175 bar) can ‘peel back’ steel tubing rather effectively.
Back to the stale air bit.
Does it matter? Having a charge of air compressed for a long time?
If you were going to breath it I’d say yes but otherwise no.
Except if the air was damp when it was put in.
Then there may be a deterioration of the metalwork.
Only it’s not the air that will cause the problem, just the water vapour.
Does wet metal rust under pressure?
Yep, pressure or not,
shit rust happens.
Only how can you tell? It’s simple, you can’t “easily”.
Some fire a few clean patches through the weapon looking for the telltale brown smears of water vapour. Others have been known to strip the air reservoir down for a visual inspection.
Which is something I’m not in a hurry to do.