Depends. The alloy matters, I think.
Once upon a time I had a TC Greyhawk that was pissing me off somewhat, so I left it loaded for about three months with Goex FFG. Don’t recall if I had fired it before that or just popped caps. Anyway, when the trial was over, I picked the nipple, repalced the cap, and it went kerblowey just fine. No sign of any damage in the barrel.
Later, I bought another one, NIB, and it had little black spots on the outside that clearly were some sort of corrosion, almost etched, and the devil to remove. My newest inline is a Knight, nitrided over SS. That’s about as good as it gets, I think.
