On my last barrel I used an ammonia wash, it was still rusting, did it again, it was still rusting, gave it a baking soda scrub, it was still rusting, did it again and it was still rusting. I was assured by the folk here that it would stop on its own and it did a few weeks later for the most part although I did card it one more time about a year later.
I heated the barrel and flooded it with motor oil after ever neutralizing session.