I'd expect it bed in & the power raise over the first 1000 or so & stay that way for a good number of years.
Just say, if you had a new spring rifle of reputable make, and fired 500 shots of the same make of pellet per week, how long would it be before it showed on a chronograph a power lost of 1ftlb ?
Just curious as to the time a spring becomes weakened as to loose power.
I'd expect it bed in & the power raise over the first 1000 or so & stay that way for a good number of years.
It can depend on the gun and batch of springs, I once acciedently left a TX cocked for months and it was fine, but the factory spring on my old type 80 collapsed in power a very short time of normal use.
TX springs seem very consistent quality, also the springs on long stroke guns seem to last longer, perhaps because they are under less stress.
HW77K .22, HW100KT .22, HW95K .22. AA TX200 MK3 .22. AA S410 MK3 .177. HW80 .25 HW30S .22. Pistols: Walther CP88 .177, Hatsan Mod25 Supercharger .22, HW45 Silver Star .177, Webley Alecto .177, SMK Victory CP2 .22
It depends on many factors, the state of the piston washer and the type of pellets being used. Even the way it is cocked might make a difference, a very rapid snatch might cause premature wear.
I think if it was a rifle with a well bedded-in piston washer, with pellets that caused neither slam nor too much bounce and with a good quality spring, you could expect to shoot 20,000 to 30,000 pellets (40 to 60 tins) before the power started falling off.
Some rifles like the old Feinwerkbau 300s had piston rings and very low-stressed springs and they would las for hundreds of thousands of shots. Similarly, old leather-piston-washer rifles, once run-in will keep going forever with just the odd drop of oil and a new spring every 20,000 rounds.
The best thing to do is to fit well-fitting guides to a good quality spring, lubricate sparingly but correctly, cock the rifle smoothly and use pellets which suit the rifle's cycle well, not too heavy and not too light. Dieselling, dry firing and poor quality springs will increase the likehood of spring failure or premature wear and loss of mechanical efficiency.
Check on a chrono every 4 tins and you should be fine.
I think Paul Watts, a tuner in the USA, tears down his airguns every 7000 shots and replaces the spring, but that is like replacing the engine oil on your car every 1000 miles, just a waste.