Does Cast Bullet Hardness Change after Powder Coating?

Does Cast Bullet Hardness Change after Powder Coating?

The practice of powder coating ammunition is quickly gaining momentum among the cast bullet community, and it’s not hard to see why.  Although tedious at times, powder coating bullets can reduce or even eliminate the need for conventional bullet lubes as well as further reduce barrel leading.

As most folks employ the ‘shake and bake’ method, wherein powder coating is baked onto bullets via a toaster oven, I’ve always assumed that the heat used in this process ends up annealing the bullets to some degree.  Apparently I’m also not the only person thinking this, as recently some of the internet’s more  prominent powder coating proponents have begun water-quenching their bullets as soon as they leave the oven.  Although I’m sure that helps regain some of the lost hardness, I suspect there’s still a net loss, as bullets exiting the oven are nowhere nearly as hot as those leaving the mould.

With that in mind I decided to conduct an experiment to determine whether or not powder coating actually changes the hardness of cast bullets, and if so, how much hardness can be regained by quenching them afterwards.

Method

For this experiment, I used Lee Precision’s Lead Hardness kit to test some .44 caliber bullets, all of which were cast on the same day, using the same equipment, and from the same wheel-weight alloy.

Additionally, I’ve decided to further break things down by testing bullets that were air-cooled vs those that were water-quenched when cast.

Non-Powder Coated:

Air-Cooled

The first thing I needed to do was to establish some baseline figures for each type of bullet.  I did this by taking measurements from bullets that were NOT powder coated, so that I’d have something to compare to.  Beginning with the bullets that were air-cooled when originally cast, the measurements were as follows:

Bullet 10.064″12.5BHN
Bullet 20.066″11.8BHN
Bullet 30.064″12.5BHN
Bullet 40.066″11.8BHN
Bullet 50.064″12.5BHN

That gives us an average of BHN 12.22 for the non-powder coated, air-cooled bullets.

Water-Quenched

Next I proceeded to obtain a baseline for the non-powder coated, quenched bullets.  The measurements for these were:

Bullet 10.044″27.2BHN
Bullet 20.044″27.2BHN
Bullet 30.044″27.2BHN
Bullet 40.044″27.2BHN
Bullet 50.044″27.2BHN

That leaves us with a BHN of 27.2 for the non-powder coated, water-quenched bullets.


Powder Coated:

Air-Cooled/Air-Cooled

Moving on to the powder coated bullet tests, I began by testing the bullets that were air-cooled when cast, and then air cooled again after powder coating.  The measurements for these were:

Bullet 10.064″12.5BHN
Bullet 20.064″12.5BHN
Bullet 30.064″12.5BHN
Bullet 40.064″12.5BHN
Bullet 50.060″14.3BHN

That gives us an average BHN of 12.86 for the powder coated bullets that were air-cooled when cast, and air-cooled again after coating.

Air-Cooled/Water-Quenched

Next, I decided to test some bullets that were air-cooled when cast, and water quenched after coating.  The measurements for these were:

Bullet 10.050″20.9BHN
Bullet 20.050″20.9BHN
Bullet 30.048″22.7BHN
Bullet 40.050″20.9BHN
Bullet 50.048″22.7BHN

That leaves us with an average BHN of 21.62 for the bullets that were air-cooled when cast, then water-quenched after coating.

Water-Quenched/Air-Cooled

Now we’ll take a look at the tests performed on some powder coated bullets that were quenched when cast, then air-cooled after coating.  The measurements here were:

Bullet 10.058″15.4BHN
Bullet 20.058″15.4BHN
Bullet 30.062″13.4HN
Bullet 40.060″14.3BHN
Bullet 50.060″14.3BHN

That leaves us with an average of BHN 14.56 for the bullets that were quenched when cast, then air-cooled after powder coating.

Water-Quenched/Water-Quenched

Finally we’ll examine the data from some coated bullets that were quenched at casting, and then again after coating.  The numbers here were:

Bullet 10.048″22.7BHN
Bullet 20.046″24.8BHN
Bullet 30.050″20.9HN
Bullet 40.048″22.7BHN
Bullet 50.046″24.8BHN

These yielded an average of 23.18BHN for bullets that were water-quenched when first cast, and again after powder coating.

Results

Alright, that’s a lot of numbers, but what do they all mean?  Using our baseline values of 12.22BHN for air-cooled, non-powder coated bullets– and 27.2BHN for water-quenched, non powder coated bullets, there are definitely some interesting comparisons to be drawn.

Bullets that are air-cooled when cast, powder coated, and then allowed to air-cool again experience no appreciable change in hardness – (12.22BHN -> 12.86BHN)

Bullets that are air-cooled when cast, powder coated, and then water-quenched will yield a major gain in hardness – (12.22BHN -> 21.62BHN /+77%)

Bullets that are water-quenched when cast, powder coated, and then allowed to air-cool again will soften by about half – (27.2BHN -> 14.56BHN / -47%)

Bullets that are water-quenched when cast, powder coated, and then water-quenched again will soften slightly – (27.2BHN -> 23.18BHN / -15%)

Summary

So, does cast bullet hardness change after powder coating?  Yes, unless you’re exclusively using air-cooled projectiles, employing heat to powder coat your cast bullets has a major impact on final hardness.

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