For those that have a hard time reading fuzzy text on a computer screen the answer is cast iron boxes.
Thanks BR.

Still interested in bluing sand. Is that just plain sand held at temperatures to get a blue oxide, or is the sand infused with something to get a blue at a lower temperatures?

For anyone wondering why Krags would be difficult or impossible to build today, the article says 120 different machining operations were involved. Each one necessary and carrying the risk of scrapping the receiver.