I had used boiling hot water to rinse the barrel with. The barrel was almost too hot to handle. This was in an effort to get it to dry quickly. That probably had something to do with it. I did get the rust out, after soaking the whole barrel overnight in an EVAPO-Rust bath. No more rust, but no more blue either. That's OK though. I wasn't really satisfied with the blue job anyway. I left it in the white so if it happens again I can just swab the bore with EVAPO-RUST and let it dry in the bore before putting a coat of oil in it for storage.