I have 40K rounds on my 9mm Core, still has the original recoil spring, I have a spare in my range bag that is collecting dust. To me this proves that the flat wound springs are markedly better than the round springs. I've never had a coil spring last this long. I've considered using the Sprinco "recoil reducing" spring a few times, but then I reconsidered and didn't want to mess with something that (for me) was a non problem.