I've had my old M1 Carbine for over 30 years. It's a '43 Underwood that I bought at a garage sale when I was in high school. It's nothing fancy, just an old Blue Sky refurbished import. I've fired many thousands of rounds through it over the years, jacketed and cast.
I'd never really given any thought to springs until recently when I was pondering how sluggish the bolt felt. I got on Ebay and spent $10 on a new spring. It sure made a big difference. My cast bullet load now just drops the empties onto the bench beside me.