Years back I was calling Turkeys for a friend who never got one. Beautiful Tom came strutting in. At about 15 yards he decided to take the shot, and click, nothing. The Tom went running off and he sat there perplexed, scratching his head.
It seems his Remington 1187 had been stored for many years cocked. We tried numerous round after that and the firing pin would just leave a little mark on the primer.
He changed the spring and was good to go. I know it's a different spring than a magazine spring, but it did wear and fail to work after sitting for years.
All that being said it could have been gummed up, but knowing this guy and how miticulous he is I find that hard to believe.