Okay to store airguns in the cold?

When hunting I've always let my rifles, be they powder burners or air, acclimate to the temperature I'm hunting in before setting afield, and usually not out for more than 6 hours at a time. Today I tried using the HW30 on some HOSPs, but the POI was off after I had just sighted it in. After 10 or so shots it would start to group, but another break and again it would be off target. I've used this rifle all summer pesting HOSPs and never ran into this. Is this caused from leaving it in the garage 24/7 in sub freezing temps at night and then 30s to 40s in the day? Should i keep in the house and bring it out when needed? 

Because of this, I brought out the Daystate Regal and set it up. I took a few shots and it was spot on, but will it be still be on after a cold night in the garage? Will keeping it and /or the HW in the garage for long periods in below freezing temps hurt the seals?

I brought the HW inside for the night and I'll try shooting it tomorrow and see if the 1st shot is on target.


 
It is likely expansion and contraction of metals, similar to scope shift in heat, causing the issue. You will have to experiment with the particular gun to see how to overcome this.

I have been experimenting with cold weather effects lately. I try to let it get cold to ambient temperature before the shooting session. It goes into the cold to acclimate for at least an hour before shooting. The gun is frosty and wet when done, but I think it is because of the fill tanks air being hotter than ambient temperature and also the effects of compressed and expanding gasses at the shot. The big tank is somewhat insulated so it doesn't get as cold as quick. I bring the gun inside and give it a thorough wipe down and set it in front of the warm air vent to warm and dry. No issues with water, corrosion or flash rust on anything so far. And because of sighting in with cold weather it tends to stay true.
 
As above, also oils and grease become more viscous, the piston seal and barrel seal become less flexible, this may account for inconsistencies until the repeated shot cause the piston to warm up and the gun to stabilise.

One other point, bringing a cold gun into a warm room can cause any moisture in the air to condense on the metal, I always wipe my gun over with an oily rag as soon as I get in and again an hour or so later.



Bb
 
I have had this issue with a Springer, It did not like cold temps I think it had more to do with thick oil on the spring than anything else but could also be due to steel shrinkage. As you said the NP2 does not have the issue this is because the Nitrogen is not effected by colder temps like that of O2 and there is not any metal springs being effected by the colder temps 

It may not be a great change but keep in mind that steel shrinks when cold, you might be surprised by just how much it can shrink. We used to freeze steel pins on dozer tracks to get them into the holes. If you didn't you would never get the pin in no matter how hard you beat on the thing. 
 
Not an air gun but high pressure air. GE made a circuit breaker for High voltage applications that used High pressure air. The compressor package lived in a cabinet with a heater and thermostat. I have made thousands of dollars when a breaker in a remote location lost heat in the winter. There have been times that the outage would put customers out of power. To temporarily fix a leak we could heat the leaking area with a heat gun or propane torch. After the leak stoped we would fix the cabinet heaters. Then come back another day to fix the air package. You will avoid problems if your air guns stay in comfortable environment when possible.