I'm an idiot, but at least I learnt somethin

I have a TX200 in .177 that I got used on the forums here a year ago. The stock was beautiful but the previous owner was pretty rough on the blued finish, lots of scratches and some surface rust. He made no mention of it, in fact claimed the opposite, and when I got it it kinda pissed me off. Take away from that is to get as many pics of the gun before you buy cause your definition of "no issues, great condition" and someone else's are not going to be the same. That said I do believe I got it for a fair price considering the cosmetic issues.

Now besides that the gun shoots amazing. It will put as many rounds as you want into a group that can be covered with a dime at 40 yards. I had it out shooting this past summer, probably late july, early august, and I got a 10 shot string avg of 913 with a sd of 3 and es of 10 shooting 8.3 jsb. That was the last time that I shot it, because deer season was coming in and that took precedence. I didn't get anything with my bow this year but I have gotten one with my Raptor .30. We only have a month left, so fingers crossed for one more. Anywho, saw the shoot a corn kernel challenge and thought, I'd give it a go. Grabbed the TX200 and went out to the deck. When I went to cock the gun the cocking lever basically just free fell to the bear trap. There was no resistance. I panicked for a second and then realized immediately what I had done. I never fired the last shot from the summer. There was still a round in the breach. The spring had been compressed for 4 months! Oh, I'm so dumb. I forgot all about the corn and broke out the chrony. To my relief and pleasant surprise, I got a 10 shot string with avg of 894, sd of 4 and es of 12. Now I'm not saying it is ok to leave your springer cocked for 4 months at the time, but I can attest that it made no difference in my case. I used to be worried about leaving it cocked for an hour or two if I was out after squirrels or something, but now I can put that to bed. The saying goes something like a wise man learns from his own mistakes, but a wiser man learns from the mistakes of others. So I'm handin out free knowledge. Still gotta go shoot that corn.
 
You are a lucky man, I have left them cocked for a day or so with no real loss of power, but 4 months is a long one. Great learning experience here !!! It really comes down to the spring and how it has been treated and tempered in its mfgr. Having worked with metals as a toolmaker for over 50 years spring technology has improved greatly from 25 years ago! Mfgrs have had to create super springs for use in car engines that today can turn 8k rpm all day long, think how many times that valve is opening and closing every second!!! Much of this science has been drawn into spring gun springs. I can remember when springs were lucky to last 5k shots, really lucky!! But in the last mabey 10 years you can get at least 10k to 15k shots from a decent spring. Factory springs are usually cheap and short lived with the exception of AA, their sorings have always lasted longer than other mfgrs from my experience, probably due to a very low preload. We now have great sources of quality aftermarket springs which give even better life, however, you can always get a bad one. Spring metalurgy is not an exact science yet, but has improved greatly in the past decade. Folks need to remember to smooth and polish the spring ends to allow the spring to rotate freely , if not you will shorten the life of any gun spring, something the factory still does not do.
 
If you look into it, the consensus of many spring gurus is that it is not compression that kills or weakens springs, but the cycling of them is what makes them weak.

It may have something to do with the quality of springs so I am sure there will be people that disagree with the above and state that their compressed spring indeed did loose some punch.

This apparently did not happen with your TX200 spring. 
 
I recall someone doing empirical testing on various spring guns by leaving them cocked for various time periods (up to several months) and then testing power versus a baseline.

The results were consistent with your experience. Concerns about spring guns losing power when left cocked are typically overblown, especially for the timeframes consistent with how these guns are actually used.

R
 
A topic that intrigues many of us that keep some number of magazines loaded for extended periods of time. 

The problem with studying the long-term effects of leaving springs compressed versus uncompressed, frequent versus infrequent compression/decompression cycles, is that it takes so much time to gather the data. 

In addition, spring-air gun spring cycles are very different than magazine cycles.

Perhaps a time machine would facilitate the analysis.