That's not rust, or at least not rust from where you think it's from.
The barrel is aluminum. Anodized aluminum doesn't rust.
Now the bolt and air chamber are steel, those can rust, which gets in the lube and can spread down the barrel. The detents are also steel, and have a tendency to rust as well. And possibly the tube inside do the front shroud, I'll have to check mine.
Anyway, any brown crud you find just means the gun needs a bit of cleaning and re-lube.
So lets get to what the gun is actually doing. So the gun is firing, but not feeding paint from the mag?
David Johnson, AKA Fubarius.
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