Most of them bend...increasing friction which slows the gun down and gives it a rough cycle. Some do shorten over time, exp. those with a good bit of pre-load (pre-compession).
Not too big on springers, but keep a couple of old friend about the place.
Oldest gun of which I am the only shooter (bought new) is a bit over 30years old. On its 3rd spring, but the two issue Web. springs were probably poorly tempered as they both snapped.,,then again, it took about 12 years per spring, so I've really no complaint.
(However, when this set of piston rings dies (yes...has rings), am probably screwed).
Never shot my .177 RWS34 as heaviy, but it does see use. Will be 19 next month, still on the issue spring.