Brinell Hardness….Testing Your Alloy

Testing Your Bullet Metal

The first step, before even firing up your melting pot, is to test the metal you’ll be working with.

Just how hard is the alloy?????  Lead has to be reasonably hard to grab the lands in the barrel (to impart spin to the bullet).  It also has to be reasonably soft to obturate .  SO WHAT IN THE HECK IS “OBTURATE”???? The word simply means that the bullet has to deform to some degree to form a tight seal between the driving bands, and the full inside diameter of the barrel.  The chamber pressure will cause the lead to form to the barrel.

So……..why does the bullet have to seal the barrel???  First, it has to prevent hot gas from escaping……it’s what pushes the bullet down the barrel.  Second, it has to form a tight enough seal that the combustion gases don’t sneak around the driving band, act like a cutting torch, and cause molten lead to deposit in the barrel (referred to as “leading”).  Leading can so foul a barrel that it can cause excessive pressure in the barrel/chamber due to the bullets inability to travel properly down the barrel.  This can lead to bad things.  Exploded barrels, trips to the ER, etc.

The Tools

I use the Lee Hardness Tester, not saying it’s the best, just what I use.  Mainly because it’s affordable, and is pretty darn accurate.  A brief description of the tool  They can be purchased from many sources.

The spring loaded plunger has a hardened ball tip to indent the metal.  Because down pressure is regulated by the reloading press (by means of a spring within the plunger assembly), the indention will be the same for a given hardness lead, no matter how many times the test is repeated, and no matter how many different samples are tested.

Although the kit comes with an anvil for testing individual bullets, after they’ve been cast………full ingots can be tested prior to casting.  I prefer this method.  Why go through the effort of casting bullets that might be the wrong hardness????  Better off to test the metal beforehand.

Mount the plunger in your press.brinnel hardness1Find a good flat spot on the ingot for the indention you intend to make.brinnel hardness2Hold pressure on the plunger, per the instructions from Lee.  You’ll wind up with a nice round impression.brinnel hardness3Use the supplied microscope to determine the diameter of the impression (it’s got calibrated optics, like a rifle scope).brinnel hardness4Make sure to point the cutout towards a decent light source, this thing takes a healthy amount of light to deliver a decent image.brinnel hardness5Carefully determine the impression diameter with the internal scale in the microscope, then use the number you generated to determine the hardness of the metal.  Lee has a chart with corresponding data which matches the microscope scale.brinnel hardness6

So, What Does It Mean

I do not, for one minute, take the results as 100% accurate.  That’s just me though.

INSTEAD…….I use the numbers as a benchmark.  I know that a certain hardness (per the chart) will perform well in a particular caliber.  A 38 Special requires relatively soft lead, same as the 45ACP.  Higher pressure loads will sometimes require a harder bullet.  (Always verify by testing in your gun before racing off to find stuff to harden your lead)

The lead I tested in this example is from the batch of range lead, and some wheel weights, that I reclaimed on the previous page.  The scale gave me  a  number…… .068 .  This tells me that the ingot contains lead that’s approximately Brinell 11 .  This is plenty hard for  low pressure/low velocity loads for my .38, and my 1911 45ACP, and surprisingly good for high velocity/pressure loads in the .357, and .44 mag.  I know this from previous results casting/firing bullets made from this hardness of alloy.

Don’t get hung up on the new “hard cast” craze, see what works well in your particular gun.  You will find that softer bullets work very well with proper lube.

Hardness Changes With Time

If the ingots are air cooled, they will gain hardness over time.  It pays to test after 48 hours, and at a weeks time.  More tests at a later date are required if you intend to let loaded rounds sit on a shelf for long periods.  For my purposes, I go with about a 2 week test period.

Water cooled ingots will be harder immediately, but soften with time.  Again…….test over the desired period if the ammo will sit on a shelf for long periods.

Hardness can be increased/decreased according to your needs.  That’s a subject for a later date………how to make up a working alloy for casting.

Meanwhile I know I have about 10# of good lead for some bullets that will be used in the majority of the loads I run.

misc,_stuff_020Any day above ground is a good day


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