Does Cast Bullet Hardness Change over 1 Month?

Does Cast Bullet Hardness Change over 1 Month?

It’s been a month 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?  Lets go ahead and test five bullets from each group and see how they stack up.

Method

As with the previous experiments, five bullets from each group will be tested using the Lee Precision Lead Hardness test kit.

Air-Cooled

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

Water-Quenched

Lets take a look at the water-quenched bullets next.  Our measurements for those were:

Results

The air-cooled bullets are now showing an average BHN of 15.6.  That’s quite a bit harder than the 11.16BHN they were cast at a month ago.  We’re also starting to see more consistency among the measurements as compared to after just a week.  The hardening seen in the water-quenched variety has clearly begun to slow.  At an average of 27.74BHN, they’re still much harder than the 22.76BHN measured when they were first cast, though nearly identical to their one-week measurement.

Summary

Does cast bullet hardness change after a month?  Absolutely; the air-cooled bullets have steadily hardened by 40% in the last month.  The water-quenched bullets may have softened a tiny bit in the last few weeks, but are still 22% harder than they started a month ago.

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