Your red powder is outgassing nitric acid gas. The acid gas is removing the lining from your can.
Single based powders are made of nitrocellulose. Nitrocellulose decomposes to a lower energy molecule, releasing nitric acid gas. Nitroglycerine accelerates this decomposition, which is why the Army scraps double based powders at 20 years, 45 years for single base.
These dates are based on risk. Powders go bad before and after these shelf life dates. I have some IMR 4064 powder that I bought new in Jan 1990. It has been stored in cool dry conditions. Little, rice kernel sized tarnish spots were all over the inside of the can. The old ether smell was gone. I am loading that powder up and going to be shooting it soon because it is on the way out.
Your powder is on its last legs. The stuff will shoot, but it will also ruin cases. The nitric acid gas will cause green corrosion on bullets and create case neck cracks. I had to toss 700 LC match because the deteriorating surplus powder ruined the cases. Incidentally, the rate of the reduction/oxidation reaction increases over time.
Deterioration may cause weird pressure curve shifts. As the powder chemistry changes through deterioration, the burn rate will change. For double based powders, the surface becomes NG rich, and the initial burn rate increases, even though the overall energy content of the powder is less. Which means you can have a pressure spike even though the exit velocity of the bullet is not abnormal.
I am lacking information on single base powders, the Insensitive Munitions guy that I am learning from, he is not available. But based on my experience, I think the same issues happen in single base.
I have shot deteriorated IMR 4895 and IMR 3031. The can from which the IMR3031 came from, when I poured the stuff into a measure, a cloud of red particles floated in the air! (I suspect only some of it was rust) The stuff shot well but I have had muzzle blasts of different sound/intensities. And I have had stiff bolt lifts with charges that were grains from maximum. Something is going on, and it is not good.
There are people out there how believe the shelf life of gunpowder is infinite. This is not true.