This subject is the beating of the dead horse when it comes to springs in powder burner magazines.
Examples : AR and AK.
I am of the belief that a compressed spring used in the application in which it was designed will have no major ill affects on the spring or surrounding components.
So if you cock your gun in anticipation to shoot a rat in the evening. But the rat never appears. So your gun stays cocked all night. No big deal.
The only safety issue is that you or anyone handling the gun needs to be fully aware that the gun is cocked and loaded.
Im not trying to debate what’s right or what’s wrong. And I am not an engineer. This just my own opinion.
You cant compare a firearm to an airgun. Firearm uses powder. So when the hammer hits the center back, it set off the primer and gun powder. So leaving a firearm hammer cock have no effect on it's speed. For airgun, there is pressure behind the valve. The hammer is being push by the spring. The force it hits on the valve depend on the spring. Having a spring cocked for a long time will weaken the spring. A weaken spring won't have enough force to open the valve as a good spring. So speed will suffer. Leaving a hammer cocked for a day or two you probably won't see much different in speed. But try leaving the hammer cocked for weeks, months, years..and come back and tell us. So to make it short. It depends on how long you leave your gun cocked. A gun left a day will be much different than a gun that's been left cocked for 8 months.
Wrong, as you said above. You can compare a spring to a spring. Much has been written about this, including actual tests of actual air rifles by Tom Gaylord and others. Air rifles left cocked for multiple days (approaching a month as I remember) showed little to no velocity loss in Gaylord's testing. And what a manufacturer recommends for warranty reasons can be quite different to what is possible. I never leave my springers cocked long term but it is more a safety based idea than a spring fatigue idea. I do however have handgun and AR magazines that are now years old and that have remained loaded for multiple months at a time with no ill effects-all still function as they were designed. None have failed to feed. It should be similar with air gun springs, especially if they are quality springs.
As an aside, I recall reading an article in either American Handgunner or American Rifleman quite a few years ago regarding some WW2 vintage .45 ACP magazines that were discovered in a foot locker that hadn't been opened in decades. They had been loaded when put in the locker and had remained that way for many years. They still functioned reliably. Seems there should be no difference in most air gun springs, whether spring-piston springs or hammer springs for a PCP.
