I used to Hunt with My ML with a Clean Barrel and then mabey twice at the end of the Season I stored it for mabey 10 Months like you, but both times it shot just fine. But I Always cover the end of My Barrel with a Pice of Masking Tape to prevent Mositure from entering it and fouling the Powder.
But now I found that My ML shoots just where I aim when the Bore is slightly fouled (after shooting it once) so now I no longer would store it without firing it and cleaning the Barrel and Oil befor storage.
You could very well have Rust in it if it was fired, then reloaded then stored for 10 Months. Clean it and look inside and then you'll know for sure if there's any sign of Pitting.
You cant always go by the Color of your Patch after Swabbing, sometimes there's a reaction to whatever you use and causes the Patch to be Brown even though it's not Rust but appears to be so.
I have seen a few MLers go Bad after what you described you did though.
(BP)