NSS normally stocks the more popular chamberings on the shelf, but if demand supersedes supply before his next order comes in they obviously can't ship what they don't have on the shelf. If what you ordered is a non-stocked item they order it from Criterion as a special order and thus it has to be made and shipped to them before they can ship it out to you.

And no, they don't do any machining on the barrels at NSS, they're just a retailer.