The real trick to getting a consistant and repeatable straw, fireblue or anything in between is to do it like they did back then. Brownells has some molten salt blue salts. They are a nitrate salt that is heated in an iron pot to a specific temp depending on the color desired. You can use a quality high temp thermometer to measure the temperature and by maintaining it consistantly you can insure that your straw doesn't go to blue while you try to get it cooled. The molten salt blue also has more consistant coloration because there is no contamination from various gasses or materials you might have in your oven, on your sand or in your heating device. Here is link to brownells page with the Nitreblue salts.
http://www.brownells.com/.aspx/pid=1...E_BLUING_SALTS
I have no affiliation with brownells other than as a user of their products. I've used this stuff for quite some time with good results. The only real warning I've got is don't let the salts cool with your parts in them. Its a pain to get the parts out of the solidified salts, you have to reheat. Quenching after dipping removes the salts so there is no real cleanup required
Hope that helps
Biff