Quenching Cast Bullets with Chilled Antifreeze and Brine

Quenching Cast Bullets with Chilled Antifreeze and Brine

As a followup to my recent tests with quenching cast bullets in antifreeze and brine, I decided to do a pair of secondary tests using chilled versions of the same fluids.  One of the advantages to both these liquids is that they can be cooled below the freezing point of water, potentially increasing the temperature differential between the coolant and the bullet.

Method

For this experiment I took 1/2L each of standard automotive antifreeze and 8:1 brine, and cooled them to -25C/-13F for 24 hours.

As with my other tests, I cast all my test bullets from the same alloy using the same equipment in the same session to eliminate outside variables.  In addition to the test coolants, I’ll also established a baseline by casting a standard water quenched set of bullets as a control group.

Once the casting session was complete, five bullets from each group were tested and averaged out using a Lee Precision Lead Hardness test kit.

Water-Quenched

Beginning with the water quenched control group, the readings were:

Bullet 10.060″14.3BHN
Bullet 20.058″15.4BHN
Bullet 30.058″15.4BHN
Bullet 40.058″15.4BHN
Bullet 50.056″16.6BHN

With an average BHN of 15.42.

Chilled Antifreeze

Moving down the line, the results of the chilled antifreeze bullets were:

Bullet 10.055″17.2BHN
Bullet 20.056″16.6BHN
Bullet 30.055″17.2BHN
Bullet 40.056″16.6BHN
Bullet 50.056″16.6BHN

This yielded an average of BHN 16.84.

Chilled Brine

Finally we have the chilled brine test, which stacked up as follows:

Bullet 10.053″18.6BHN
Bullet 20.053″18.6BHN
Bullet 30.053″18.6BHN
Bullet 40.053″18.6BHN
Bullet 50.051″20.1BHN

…and an average BHN of 18.9; substantially higher than the control group.

Results

Based on these results, bullets quenched in chilled antifreeze showed an increase in hardness of about 9% vs the control group, while chilled brine saw gains of about 23%.

Summary

Although chilled antifreeze did perform better than water, I don’t think it outweighs the hassle of having to clean the bullets afterwards (which is surprisingly finicky).  Chilled brine on the other hand performed surprisingly well.  With an improvement of 23% over the control group, this could have some potential.  Being as table salt is cheap and easily washed off the bullets, I could see chilled brine being a worthwhile quenching fluid for folks driving high velocity rifle rounds and really need the extra BHN.

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