Training the Budding Gunsmith–Fire Blueing

By Justin Ledgerwood,
GCA Silver Member

We all look for ways to show our uniqueness; the way we dress, or do our hair, or for some of us, our beards. Our firearms are no different. I don’t like knowing that my rifle looks exactly like a thousand others. So we try to add our own flair, to set ourselves and our firearms apart. This can sometimes be very time consuming or costly. 

Items needed:

  • Screws
  • Propane torch (or equivalent item)
  • Pliers (or equivalent item)
  • Various grinding & sanding implements • Used motor oil (or equivalent item)

One easy way to do this inexpensively is by fire blueing your firearm screws.  Fire blueing works by heating the metal to a specific temperature. The temperature can easily be seen by the color the metal turns. When steel reaches about 390 degrees Fahrenheit it will begin to turn a light shade of yellow. Between 555 degrees Fahrenheit and 625 degrees Fahrenheit it goes through the stages of blue. This is the color I will be  attempting to reach.


Temperature/color chart

For my example piece I will be using a large carriage bolt that is easier to see.  The first step I took was to grind down the lettering on the bolt head and progress through the various sandpaper grits until it produced a nice polished surface. I probably shouldn’t have polished the bolt so much as it was very difficult to get decent photos.


Original carriage bolt used for this demonstration

Once your screws are brightly polished you want to find something to hold the screw while you torch it. You want something along the lines of forceps or a padded pair of pliers, just something to hold the threads and not damage them. Keep a small container of oil close by so that you can immediately quench the screw  once the proper temperature (color) is reached to keep it from progressing. Used motor oil will work well, or gun oil. The idea is to use something that will sap the heat from the screw very quickly.

Once you have everything set up, use your holding tool and pick up the screw by the threaded end. Light your torch and slowly begin to move the flame over the head of the screw. Once the temperature reaches right around 380-390 degrees it will, quite suddenly, turn a light straw color. If that is the color you want your screws you would immediately quench your screw by plunging it into the oil and letting it cool. If you want a different color you would continue to hold the screw to the flame until the desired color is reached, and then quench.

There is some small amount of talent involved with capturing the exact color you want. The trick is to remember there is a sort of lag in the rising temperature and color change. When the metal reaches 390 degrees it will suddenly turn straw yellow, and as the temperature rises (in approximately 20-degree intervals) it will go through slight shade differences. Then, all at once, when it reaches about 470 degrees it will jump to brown and quickly move through the various brown shades.

The difficulty lies with spotting the differences in shade. When you have the flame to the screw it can be difficult to see when the metal moves between shades. So while you are looking at a brown screw head one minute, it may have already been through all the brown shades and then suddenly jump to the blue. You have to stay on your toes, and move the torch back and forth. This allows the heat to spread evenly and also gives you a glimpse at the screw head without the flame in the way.

After you have reached the desired color and quenched the screw, all that is left is to clean it up and reinstall after it completely cools. If you happened to have missed the color you wanted it is a very simple fix. Just re-polish the screw head and try again.


The final blued and polished bolt head

This process can also be used for other parts of the firearm, but unless you know exactly what you are doing, seek the help of a professional. Tampering with the factory temper of certain parts can be very dangerous.

Another simple project down, a few thousand more to go.  If you have any comments, questions, or ideas, please feel free to email me at

As always, be proud of what you do, and put your name on your work.

One Response to Training the Budding Gunsmith–Fire Blueing

  1. Good article.
    I like the “Approximate Temperature by Color” graph.
    The part can also be quenched in water (instead of oil) since it is only being annealed and not hardened.
    Thanks for the article. Cheers.

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