I accidently allowed one of my match 1860 Piettas go over 90 days without cleaning. I had broken a handspring, repaired it and put it away with no further thought. Our next two shoots were weathered out. When I got the guns out for the next match I discovered the mistake. I had been shooting GOEX.
Wiped the outside of the gun down with a Ballistol rag. Wiped the face of the cylinder off. Turned a mop in each chamber, pulled a bore snake thru the barrel and I was good to go.
Absolutely no damage.
Oh, yes! This is in southern Missouri and we do understand humidity.