Alloys....How hard is hard enough?

Bullet "hardness" is another common complaint some commercial bulletmakers hear about, and some for good reason! What got me into commercial bullet casting in the first place was that box of swaged .38 slugs which smeared lead down my .357 bore from forcing cone to muzzle.

Some bullet suppliers claim some pretty outrageous Brinell hardness numbers and antimony percentages. The fact is that the local lead supplier, for the most part, determines what is available. The lead suppliers are pretty sharp people, at least mine is. He is an expert in most recyclable metals and has a thorough understanding of the various properties and interactions of those metals. The suppliers have, thru the years, scienced out the bullet alloys and have all pretty much standardized their alloy offering to us commercial casters.

Lead, the obvious main ingredient, is given strength and rigidity (hardness) by the addition of the element Antimony. The more Antimony in a lead alloy, the harder it becomes up to around 23%. In the past five years, Antimony content in commercial bullet alloys has been reduced to about 6 % to help keep costs down industry wide. At that percentage the alloy still makes a bullet that's hard enough for all but the most recoil hungry velocity mongers. Tin, the most expensive component of bullet alloy, fortunately is required in only a small percentage. It has long been established that only 2% tin is adequate to make the molten alloy flow out into the extreme corners and irregularities of the bullet mold. This is what gives us a nice, sharp driving band in a mold cut to give one. Some commercial casters may re-smelt their lead in small batches to add Antimony to the mix. Understandably, this must increase the overall cost of this alloy and ultimately, your carton of bullets.

For consistency, I prefer to trust my supplier. It's in his best interest to give me a consistent alloy lot after lot after lot. He has a $500,000+ spectrographic analyzer which he uses to monitor each batch of metal and can control the presence of impurities and trace elements (some of which, in specific amounts, are desirable in the casting process) such as sulphur, potassium, aluminum, zinc, iron, cadmium, calcium, arsenic, and copper down to the thousandth of a percent or better. By the way, for you health conscious reloaders, presence of Arsenic in bullet alloy is very, very small. So small, in fact, that the Antimony present is more of a health concern than the Arsenic!

Foundry alloy offerings vary somewhat throughout the U.S. but one thing that is a sure bet: the higher the percentage of Antimony in an alloy, the more expensive it will be. This is a cost that is passed along to the consumer. If a bulletmaker is claiming a Brinell hardness number of 22, someone is paying for it, so the consumer should definitely hold the bulletmaker accountable. When considering the super-hard alloys, (and they do have their place) it is wise to know and be realistic about what you NEED.

From Lyman's The Cast Bullet Handbook:

Composition & Hardness of Common Bullet Metals

Alloy

Lead

Tin

Antimony

BHN

Linotype

86%

3%

11%

22

#2 Alloy

90%

5%

5%

15

16-1

94%

6%

0%

N/A

10-1

91%

9%

0%

11.5

Wheelweights

95.5%

0.5%`

4%

9

Pure Lead

100%

-

-

5

Just as with steel, lead's mechanical properties vary predictably, and proportionally with the type and percentage of alloys present in the metal. Using this table, you can interpolate and find approximate expected Brinell Hardness values for different Antimony contents in a bullet metal.

Don't confuse the Brinell Hardness number with the Saeco Hardness number. The scales are totally different. Saeco Hardness uses 0 for pure lead, and 10 for Linotype.

There's nothing magical about bulletcasting. Reloaders have been casting their own bullets for years. I am equipped to do it on a larger scale and, as a result, can supply others with a quality bullet for a reasonable price. Your web search brought you to me because you are seeking a volume of quality bullets and because you are choosing not to cast your own.

For many, many years shooters around the world have relied upon the traditional lead bullet hardened by the addition of antimony. It has been found to be the most consistent, reliable, and cost effective alloy available. I would put my bullets up against any of these exotic alloys any day of the week when comparing leading, consistency of weight, general appearance, cost effectiveness, and accuracy in flight!

 

What the Hell is "Virgin" Alloy?

 

What is "Virgin" Alloy? This statement has always baffled me a little. For a metal to be considered virgin, must it consist of freshly mined ore? First use? Our cars are made largely of recycled steel. Does that make them inferior in some way? What about the impurities that are inherently found in freshly mined, unrefined metal ores? To me, alloys are by definition, simply metals that are mixed in certain proportions such that their resultant mechanical, electrical, magnetic, optical, or thermal properties are desirable for a specific application.

Do the mechanical properties of bullet alloy change every time it's recycled?  No, not unless the percentage of a component metal, or impurity is altered during the remelt.  Disregarding impurities, any 92-6-2 (lead, antimony, tin) mix will have similar properties to any other alloy of the same proportions whether it be on its 1st, or 25th melting.

When comparing alloys, I prefer to examine the source of the alloy, the methods used in controlling its makeup, the impurity level, and the analysis methods rather than to simply use the term "virgin" to mean "desirable", or "good".

 

Barrel Leading

 

Barrel leading is a fact of life when shooting lead bullets, just as copper fouling most surely comes from using jacketed bullets. Some commercial bulletcasters will deny it, saying their brand of alloy/lube combination "eliminates" it. I've even heard of one bulletmaker who told his customer who experienced leading that it was because he loaded the bullets wrong! The best we cast lead bullet shooters can do is to select an alloy which will MINIMIZE leading. What causes barrel leading? I've read volumes and thought very hard about this, and have come up with several causes of barrel leading.

A rough bore will cause leading no matter how hard the bullet, no matter how slow it is driven. There is a big difference in how smooth the finish is in a brand new barrel from the manufacturer depending mainly on how the barrel was made, i.e. button rifled, cut rifled, broached, etc. Typically, what you pay for when you purchase any firearm is quality machine work. 'Nuff said.

Too soft an alloy driven too fast will cause barrel leading. When a bullet is fired, we expect a lot out of it. We expect the rifling to impart rotation to the bullet, necessary for bullet stability in flight. For the average revolver having a twist rate of 1 in 20", at 1500 fps we expect the rifling to accelerate the bullet radially from 0 rpm to 54,000 rpm nearly instantly. (I say "nearly" because the bullet does not start out at its terminal velocity). For comparison, this is slightly under what a typical dentist's drill spins, and you KNOW what they sound like! According to Newton's laws of inertia, an object at rest tends to stay at rest. This applies to radial motion as well as linear motion.

12/20 x1500 x 60(sec's/min)=54,000 rpm.

A Smith & Wesson Mod 629, having a bore of .429" has rifling measuring .009 tall (.411 across the lands).

(.429-.411)/2=.009

When the rifling exerts its radial force upon the bullet, it uses only one side of each land to push on the bullet. We are only accelerating the bullet radially in ONE direction. A S&W revolver has five of these force areas. Measuring the side of the bullet (length), after you take away the bullet nose, the lube band, and most of the crimp groove and beveled bullet base, the bullet/bore contact area only measures a total of about a quarter of an inch. (.25") out of the overall bullet length. So the total contact area on the side of each land can be found to equal:

.009" (each land height) x .25"(contact length) =.00225sq.in.

Times 5 lands = .00225 x 5= .01125 sq.in. of high pressure contact area between the bullet and the bore!

It is apparent that we are "gripping" the bullet and applying a phenomenal amount of force (required to accelerate the bullet from 0 rpm to 54,000 rpm nearly instantly) to a contact area little greater than ONE-ONEHUNDREDTH OF A SQUARE INCH!

In your mind's eye, picture the bullet, engraved into the rifling, with only 1/100 sq.in. of surface area on the outer edge of the bullet to accelerate it at this rate and you will see that there are 5 areas (the lands) where, in engineering terms, what is called a SHEER force is applied to a section of bullet only .009" deep and as wide as the land.

It becomes obvious that if a particular alloy is not hard enough to withstand this sheer force, the bullet will tend to "strip" thru the rifling, that is, the .009" high outer layer of bullet that the rifling "grips" tends to get sheared off, wholly or partially, in the celeration process. The softer the alloy, the greater the tendency for some of the bullet lead to be "rolled under" itself and deposited (smeared) on the bore as the lead yields under high loading. My experience finds that typically, more lead will be deposited at the rear of the barrel, just forward of the forcing cone, or chamber, where the bullet is just starting its radial acceleration from rest, and mostly at the base (outside) of the rifling lands where it has been force-peened into the inside edge as the bullet slides by.

 

Hard lead leading vs. soft lead leading.

 

It has also been my experience that there is a difference between the lead deposited by over-driving a softer bullet as compared to that left by an over-driven harder bullet.

Soft bullets tend to leave a dark gray smear which, covers the entire circumference of the bore. Small particles of lead sheered off the bullet by the rifling are actually "peened" into the micro surface of the bore finish. This is very difficult to remove by non-abrasive or non-chemical methods and tends to be cumulative in its presence based on the number of shots fired.

Harder bullets, when over-driven, will tend to leave very small chunks, slices, shavings, or curls in the rifling. Its appearance is pretty much the same as powder residue until you swab it out of the bore and find that it is silver-gray in color. This residue removes easily with a copper bore brush and sometimes even a plastic brush or patch. I've never found this type of leading to be cumulative as the next shot seems to purge the residue left by the prior bullet. In fact, I've got several (stainless) handguns thru which I've shot my own bullets exclusively, and have never even bothered to clean the bore! The lead deposits have never accumulated to a point where I feel they would be unsafe OR detrimental to accuracy!