stainless barrel rusting?

[Axis II]

I picked up a cva optima thumbhole stainless this year and sighted it in and left it dirty cause it shot better dirty and cleaned it this weekend. The bar that's welded onto the bottom of the stainless barrel is rusted and it will not come clean. I thought that stainless wasn't supposed to rust? would you be concerned with it being by the weld on the bottom of the barrel?

I also noticed on the receiver and the trigger guard that hopps bore blast started eating at the paint.

 

[Malachi Leviticus Blue]

It depends on the specific alloy how easily stainless will rust, but yes stainless barrels tend to rust pretty easy if left dirty.
I'd remove the rust with acid or naval jelly. There is no bluing to mess up so get rid of the rust, polish it up if you are so inclined, and clean it sooner next time. You should be good to go, assuming you haven't compromised the structural integrity.

remove any painted parts first if you don't want to mess the finish up.

 

[J-Bar]

Birchwood Casey also makes a liquid "Blue and Rust Remover" which works just dandy for small areas needing attention.

 

[Axis II]

Thanks guys.

Any clue why it's just this area? nothing else contained rust accept there.

 

[Malachi Leviticus Blue]

Presumably that's where the moisture settled. Black Powder fouling is not corrosive (if that's what you used) it is the moisture it absorbs and holds that causes the rusting.