Quenching Cast Bullets with Alcohol and Antifreeze

Quenching Cast Bullets with Alcohol and Antifreeze

Recently I’ve been thinking a lot about alternative solutions for quenching bullets.  While water is of course the standard, the fact is that many heat-treating facilities employ a number of specialty liquids to rapidly cool metal.  With that in mind I decided to try quenching some cast bullets in antifreeze and alcohol, and comparing them to a water-quenched control group.

So why antifreeze and alcohol? Alcohol interested me as a coolant for the simple fact that it has a very low boiling point.  My suspicion is that it will harden bullets faster and more efficiently than water since it boils off sooner, taking heat with it via evaporative cooling.

Antifreeze on the other hand has a very high boiling point, which is why it’s used in radiators.  While it won’t boil off the way alcohol does, I suspect that it probably absorbs heat more readily than water since it’s specifically engineered for that purpose.

Method

As with my other lead hardness experiments, each test group consists of five bullets cast from the same wheel weight alloy, using the same equipment, and on the same day to rule out any other variables.  Each bullet was then tested using the Lee Precision Lead Hardness Test Kit.

Water-Quenched

Beginning with the water-quenched control group measurements were as follows:

Bullet 10.052″19.3BHN
Bullet 20.056″16.6BHN
Bullet 30.054″17.9BHN
Bullet 40.056″16.6BHN
Bullet 50.056″16.6BHN

With an average BHN of 17.4.

Antifreeze-Quenched

Now that we have our baseline set, let’s move on to the antifreeze.  For this test I used about half a litre of standard automotive antifreeze at room temperature.

Measurements obtained were:

Bullet 10.056″16.6BHN
Bullet 20.050″20.9BHN
Bullet 30.055″17.2BHN
Bullet 40.054″17.9BHN
Bullet 50.055″17.2BHN

This yielded an average of BHN 17.96.  That’s only slightly harder than the water-quenched control group.

Alcohol-Quenched

Now for the alcohol.  Again, this test employed approximately half a litre of rubbing alcohol at room temperature.

The readings here came to:

Bullet 10.055″17.2BHN
Bullet 20.055″17.2BHN
Bullet 30.050″20.9BHN
Bullet 40.052″19.3BHN
Bullet 50.054″17.9BHN

With an average BHN of 18.5.  A bit harder than the water quenched control group, but certainly not a lot.

Results

The water-quenched control group had an average hardness of 17.4BHN.  Changing the quenching solution to antifreeze yielded a slight increase in hardness, with bullets reaching 17.96BHN.  Although this is technically 3% better than the water-quenching system, it’s such a small gain that it’s entirely within the realm of possibility that any increase is just an error in the readings.  On the other hand, the alcohol solution was a bit more effective, with an increase of 6% (18.5BHN).

Summary

So is there any advantage to quenching cast bullets with antifreeze or alcohol?

Based on these results, I think it’s safe to say that for all intents and purposes, antifreeze really isn’t any better than water for quenching cast bullets, at least at room temperature.  Alcohol fared a bit better with an increase of a little over 6%. That said, with the added cost as well as the risk associated with using something so flammable, I don’t think it’s all that practical as a serious choice for bullet quenching.

Although neither liquid performed well enough to justify their continued use, it’s worth noting they were tested at room temperature.

As both alcohol and antifreeze can be cooled far below the freezing point of water without changing to a solid state; there may still be some value in further testing at below-zero temperatures, particularly with antifreeze.

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