Does Cast Bullet Hardness Change over 1 Week?

Does Cast Bullet Hardness Change over 1 Week?

It’s been a week now since we cast up a batch of water-quenched and air-cooled bullets as part of our ongoing lead hardness testing project. Have they changed since they were first cast, and if so, how?

Method

As with the previous experiment, five bullets each were tested from the air-cooled and quenched lots.  All tests were performed using the Lee Precision lead hardness test kit.

Air-Cooled

Starting with the air-cooled bullets, the measurements were as follows:

Bullet 10.056″16.6BHN
Bullet 20.058″15.4BHN
Bullet 30.058″15.4BHN
Bullet 40.062″13.4BHN
Bullet 50.066″11.8BHN

Water-Quenched

Moving on to the water-quenched bullets, the measurements were as follows:

Bullet 10.044″27.2BHN
Bullet 20.044″27.2BHN
Bullet 30.042″29.9BHN
Bullet 40.042″29.9BHN
Bullet 50.044″27.2BHN

Results

The air-cooled bullets rated an average BHN of 14.52.  That’s a fairly significant increase from the 11.16BHN we saw when these were first cast a week ago.  It’s also interesting to note that the deviation between individual bullets is by far the greatest we’ve seen yet.  The water-quenched bullets arrived at an average BHN of 28.28, again, substantially harder than the 22.76BHN measured initially after they were first cast.

Summary

So does cast bullet hardness change over 1 week?  Definitely; the air-cooled bullet hardness has increased by 30% since they were first cast, most of which took place in the last 6 days.  The water-quenched bullets have increased by 24%, though the last six days saw more modest gains compared to the air-cooled variety.

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