Brinnell Factor

[Roland Thunder]

Can someone explaint eh Brinnell hardness factor, not in too much detail. I have some 148gr DEWC's in .38spl and they have a Brinnell factor of 10 according to the vendor (Missouri Bullet). How does this rate.

[BDS-THR]

Glen Fryxell covers this issue in chapter 3 of his free ebook and leading in chapter 7.

As you can see below, 10 BHN is soft enough to deform/obturate at light to standard .38 Spl pressures allowing you to shoot target loads without leading.

Hardness. So we want to make sure that a bullet isn’t too soft, or leading will result through galling and abrasion, and we want to make sure that it isn’t too hard so we don’t lose the beneficial effects of obturation, and fall prey to leading through gas-cutting.

Light target loads (<800 fps and 10,000 psi) BHN 6-12
Standard revolver loads (800-1000 fps, 16,000 psi) BHN 8-14
+P revolver loads (1000-1200 fps, 20,000 psi) BHN 10-16
Magnum revolver loads (1200-1500 fps, 35,000 psi) BHN 12-20
454 Casull (1400-1800 fps, 50,000 psi) BHN 16 and up

The lower end of each of these hardness ranges will expand somewhat in each of these applications. Harder bullets can be used, but they won’t obturate meaning that you’ll have to use a lube capable of sealing the system, since the bullet cannot contribute to this critical job. Hard lubes probably won’t work here. Note the recurrence of BHN 12 in many of these ranges, and remember that’s what the Oldtimers used to think of as a hard bullet.

More at link.

[jepp2]

You would probably benefit from reading the Technical Information Link at Missouri bullets.

[bossman]

With lead I like to stay in the 10 to 12 BHN range. Most of my lead shooting is for accurate low end shooting. The only time I might go to a higher BHN is for the high velocity magnum loads.

Low BHN numbers can cause leading at high velocity, and high BHN numbers can cause leading at low velocity. So it really depends on what you're going to load them for, light plinking or heavy thumpers.

[Unclenick]

Greg,

It's actually called the Brinnel Hardness Number rather than Factor. It is just a scale of material hardness same as the Vickers and Rockwell scales are, except the test methods for each is a bit different. Basically, though, they are all variations on the idea that how big a dent you can make in a test sample tells you how hard it is. The bigger the dent, the softer the material, and the smaller the dent, the harder the material.

In each method, the dent has to be made with a known amount of force pushing a particular shape probe of known size into the sample, so the result is standardized. They measure the size of the dent and plug that measurement and the pressure that was used to make it into a formula specific to the shape of the indenting probe. The result is a number proportional to how much pressure it takes to make the material give way. The more pressure that is needed, the harder the material. Thus, that proportional number represents hardness.

In the case of the Brinnel method, the probe is just a hard sphere. 10 mm (0.3937 inches) diameter applied with 3,000 kg (6,614 lb) of force is the standard test setup, but other sphere sizes and forces may be used with the formula to find the BHN associated with the test sample.

Where:

d is the dent diameter in mm
D is the indenting sphere diameter in mm
F is the indenting force applied in kg:

                  _______  
BHN = 2F/(πD(D-( √(D²-d²) )))