Just about every alloy containing lead has been used to cast bullets at
one time or another with varying degrees of success. Many bullet casters
use an alloy simply because it’s what they have available without giving
much consideration to the type of shooting the bullets are intended for.
If competition and the best possible accuracy and velocity, or hunting
bullets with a known amount of or lack of expansion are the goals,
repeatability from batch to batch of the alloy is mandatory and a
reliable, consistent source of alloy is needed, more on this further on.
Informal plinking or practice ammo and very short ranges can tolerate much
more variation in bullet alloy. Accuracy is a relative thing, what is
outstanding accuracy for one person and his type/style of shooting, his
type of firearm and his skill level would send another bullet caster
running back to the drawing board to find out what went terribly wrong.
Your type of shooting, your firearms and most important, the level of
accuracy that you are willing to accept should guide you in selecting
bullet alloys.
A very common misconception is that cast bullets lead the bore because the
alloy is too soft, in reality this is very rarely the case. Poor bullet
fit in the firearm is responsible for more leading problems than is the
alloy BHN (Brinell hardness number) being too low. Poor or improper
chamber and bore dimensions with incorrectly sized bullets and poor or
inadequate lubrication rank next in causing leading ahead of bullet BHN.
This is not to say that there aren’t soft bullets, its just not the first
thing you should think of. I did extensive BHN testing in my 9” Freedom
Arms 357 Magnum revolver using maximum long range accuracy loads. Testing
was with air cooled wheel weight alloy at 11 BHN and with heat treated
alloy of varying BHN up to 30. Many hundreds of rounds were fired in 5
shot groups at 150 meters scoped from the bench and not a single load
caused any leading, not 11 BHN, not 30 BHN. These were top end 357 loads
with a 190 gr. bullet at 1550 fps proving (in my mind at least) that
bullet fit in a properly dimensioned firearm is far more important than
alloy BHN. The only leading that I have ever been able to cause in this
revolver is with bullets that did not properly fit the cylinder throats.
As an example, the SAECO 35 caliber bullet # 399, 180 gr. TCGC (truncated
cone, gas check) is a two diameter bullet with the front driving band
.005” smaller than bullet diameter and there is no way to size this bullet
to fit the throats. This bullet leaded the cylinder (fairly badly) and
destroyed long range accuracy. The 44 Magnum was born with plain base
bullets cast of 16/1 Lead/tin alloy at 11 BHN fired at 1400+ fps and Elmer
Keith was a happy man. The popular term “Hard Cast” clouds the issue for
new casters and purchasers of commercial cast bullets and causes trouble
with both leading and accuracy when the more important issue is bullet
fit. Assuming a proper bullet BHN (not too hard) for the loads pressure
and firearm the more important issue with bullet BHN is consistency.
Shooting groups with bullets of varying BHN opens up long range groups and
increases the velocity extreme spread, consistent alloy is an important
part of maintaining consistent BHN. For the hunter using cast bullets his
alloy consistency is every bit as important as it is for the competitive
shooter. Consistency of his alloy will determine the amount of bullet
expansion (or lack of) from batch to batch and from hunt to hunt. If the
hunters alloy varies from his tested ammo his pre-determined level of
accuracy, expansion and bullet upset may not be so predictable.
|
The Four Important Metals in Cast
Bullet Alloys |
Top
of Page |
Lead (Pb)
melts at 621.3o F and has a BHN of 5. Lead alloys with some
metals very well, not so easily with other metals. Lead is a very heavy,
ductile or if you prefer malleable metal. Its weight is what carries the
bullets momentum to the target and being malleable is what allows it to
conform to the bores dimensions (obturation) and seal off the rising gas
pressure. Alloying lead beyond what is needed for the lowest practical
strengthening can have consequences in reducing the sectional density of
the bullets and this could have consequences for match loads on long range
accuracy, velocity and momentum.
Unlike most
types of steel alloy’s that become more brittle when heat treated, lead
alloy can be heat treated and made harder without adding any brittleness.
Unlike most types of steel alloy’s (or your brass cartridge cases) that
become harder and brittle when worked, lead when worked becomes softer and
more malleable. Heat treated lead, unlike steel, does NOT surface harden
but achieves the same BHN all the way through.
[2]
It is a common misconception that because they are less dense than lead,
antimony and tin may undergo gravity separation from the melt. Nothing
could be further from the truth. In the absence of oxygen or oxidizing
materials, melted lead alloys will remain stable and mixed virtually
forever. And from Lyman,
[3]Perhaps
the single most significant error in all the bullet casting literature is
the misconception that lead-tin-antimony alloy melts gravity segregate.
Lead conducts
heat slowly and contrary to the belief of some, lead does not melt from
the base of plain base bullets when fired causing leading. If it could why
don’t paper and plastic wads burn in shotgun shells? The millisecond the
bullet is subjected to this heat simply could not melt lead. Pressure
forcing the bullet against the sides of the bore could and far more likely
than this is a lack of obturation (bullet too hard) allowing gas leakage
down the sides of the bullet. This has the same effect as an acetylene
torch cutting steel and leading would begin on the trailing edge of the
rifling.
[4]
Molten lead alloy exposed to air soon oxidizes (this is NOT
gravity separation). This oxidation affects all the constituents,
including the lead. (The chemistry of tin and antimony dictates that
they oxidize at a higher rate, which accounts for their gradual
depletion from the melt.) Thus, the scum which forms on the surface
of the melt is a mixture of metal oxides, not tin or tin oxide only.
Fluxing returns much of the oxidized metal to the melt.
Oxidation occurs only at the surface of the melt (and
in the flow stream from bottom pour pots), however, within the pot
of melted alloy there are thermal currents, the coolest alloy at the
surface sinks and hotter alloy (mostly from near the sides of the
pot where the heating element is) rises to the surface. The entire
volume of alloy in the pot is subject to oxidation.
(Tin helps reduce, not eliminate
oxidation up to a max of 750o.) The bottom line,
oxidation occurs wherever, whenever the molten alloy is in contact
with air and thus the need for fluxing (fluxing returns metal oxides
to the alloy).
Antimony (Sb)
melts at 1167o F. It is the current metal used to
strengthen/harden lead alloys for bullet casters and for numerous
applications in the metals industry. It is an extremely brittle
metal but has unique characteristics in a lead alloy in addition to
its basic hardening, such as the ability to heat treat a lead alloy
bringing the final hardness up far more than what the percentage of
antimony would suggest. Alloys such as monotype (19% Sb) and
stereotype (23% Sb) are so brittle that bullets cast of them can
actually break in two by simply chambering a round or dropping it on
the floor. Antimony is a valuable part of the bullet casters alloy
but too much of a good thing is clearly not a good thing. The type
metals, linotype, monotype and stereotype, if you can still find
them, are valuable to the bullet caster for their antimony and tin
content when blending (alloying) with other lead alloys.
[5]
Antimony is a silver white metal, very hard and brittle. It has no
characteristic crystallographic surfaces when sheared. Melting
temperature is 1167°F and even when melted at or above that
temperature it is not easy to get a homogeneous alloy with lead. As
soon as the pour is started the rapid cooling causes an increasing
amount of antimony to solidify while pouring.
The addition of tin does help by providing some protection against
oxidation of the melt.
[6]
Decreasing the antimony percentage much below 4% has a dramatic effect on
the time curve of heat treated bullets. In my heat treating experiments
alloy with less than the typical 3-4% antimony in wheel weight alloy
didn’t result in softer heat treated bullets but rather, bullets that took
considerably longer to age harden and reach their final hardness, up to
two weeks longer. I found this test fascinating, reduced antimony didn’t
reduce the final heat treated BHN but rather increased the age
hardening time about 8 fold.
Lead/antimony
alloy drosses considerably. As your melt reaches liquidus temperature that
silvery, lumpy, oatmeal looking stuff floating on top is antimony.
Skimming it off seriously depletes the alloy; it needs to be fluxed back
into the melt.
Key factors of
antimony in lead alloys: Adds strength as well as hardness. Like tin it
helps pick up fine details of the mould and allows the alloy to flow
easier. It lowers the solidification temperature and raises the molten
temperature. It is extremely brittle and terminal ballistics should be
considered when choosing an alloy with a high percentage of antimony.
Permits hardening by quenching or heat treating.
Antimony can
be purchased online from the “Antimony Man” but with its high melting
point it is a somewhat arduous task trying to alloy it with lead. The
Antimony Man supplies instructions on alloying antimony with the purchase
that include the warning that the instructions must be followed precisely
to be successful. In addition, antimony is extremely toxic, when handling
it in a powdered form proper breathing protection and proper clean-up
techniques of surrounding surfaces should be used.
Tin (Sn)
Tin melts at 449o and alloys very easily with lead. Tin was
used for many years as the hardening agent in lead. In the years of
large caliber, big bore black powder cartridges the minimal hardening
effects of tin was sufficient. With the advent of smokeless powders and
much higher pressures and velocities and far sharper pressure/time curves
of the faster smokeless powders tin’s limited hardening/strengthening
effect on lead left alloys too soft for many cartridges.
Lead/tin
alloy’s age soften quickly and the higher the percentage of tin the faster
the age softening. If your lead/antimony/tin bullets are to be quenched or
heat treated (lead/tin alloy does not respond to heat treatment) the
percentage of tin will affect the final amount of hardening that can be
achieved, the higher the percentage of tin the lower the final BHN in
addition to faster age softening. Lead/tin alloy should age soften at a
fairly steady rate for 25 or 30 days and then soften very slowly after
that. Be that as it is, tin is still a very valuable addition to the
bullet casters alloy. The true value of tin for today’s bullet caster is
that it helps reduce dross during casting which enables it to reduce the
surface tension of the melt. It does this by inhibiting the oxidation of
the metal entering the mould and enabling a more complete fill-out of the
moulds intricate details. NOTE: It is not
only the surface of the melt in the pot subject to oxidation, the stream
of alloy from a bottom pour pot or casting ladle is also in contact with
oxygen and this is where tin has it's largest benefit in reducing
oxidation and aiding better mold fill-out, from the spigot to inside the
mold. Tin does add some hardening/strengthening to lead alloys but at the
percentages in most bullet alloys it is minimal.
[7]Maximum
hardness of lead/tin alloys is 17 BHN at 63% tin and 37% lead
(commonly known as 60/40 solder). Tin lowers the melting point of lead
alloys, eutectic
60/40 solder melts at 361o F. Loss of tin from the alloy from
oxidation is low as long as the melt is not overheated.
[8]Tin
provides dross protection up to about 750o and also improves
castability. Casting temperatures with alloys containing tin should be
held to about 700o so that tin’s ability to reduce dross won’t
be lost.
Arsenic (As)
Melting point, 1,503o F. Arsenic is a catalyst to heat
treating Pb/Sb alloys and only a trace is required (¼ to ½ of 1%),
adding more than this will do nothing to further harden the alloy.
Arsenic in itself does little to harden the alloy; its value is as a
catalyst in heat treating (or quenching from the mould) lead/antimony
alloys. Arsenic is of coarse very toxic but at the percentage in and
temperature of bullet alloys the risk is nearly non-existent.
However, the bullet caster should never attempt to alloy elemental
arsenic into his alloy (if he could even get it).
[9]At
the temperatures required arsenic sublimes, that is, it
transforms directly from the solid to a gaseous state, emitting
highly toxic smoke. Leave this to the experts.
In addition to arsenic
subliming
other forms of extremely toxic gases, such arsine are formed and
this should be left to the professionals. Wheel weights, chilled
shot and magnum shot are excellent sources of arsenical alloys for
the bullet caster to enrich his alloy for quenching or heat
treating.
[10]Arsenic
in combination with antimony, improves the strength. In the as cast
condition arsenic raises the hardness about 1 or 2 BHN.
Arsenic’s true value is in heat treating lead/antimony
alloys. With a trace of arsenic a much higher BHN can be achieved
while using a much smaller percentage of very brittle antimony.
Common Bullet
Alloys, |
Composition
and Hardness |
Alloy |
Tin% |
Antimony% |
Lead% |
BHN |
Arsenic |
(Trace) |
Foundry Type |
15 |
23 |
62 |
? |
No |
Monotype |
9 |
19 |
72 |
28 |
No |
Stereotype |
6 |
14 |
80 |
23 |
No |
Linotype |
4 |
12 |
84 |
22 |
No |
Lyman # 2 |
5 |
5 |
90 |
15 |
No |
Electrotype |
3 |
2.5 |
94.5 |
12 |
No |
1 to 10 tin/lead |
9 |
--- |
91 |
11.5 |
No |
1 to 20 tin/lead |
5 |
--- |
95 |
10 |
No |
1 to 30 tin/lead |
3 |
--- |
97 |
8 |
No |
1 to 40 tin/lead |
2.5 |
--- |
97.5 |
6-7 |
No |
Hard Ball |
2 |
6 |
92 |
16 |
No |
Clip-on
|
.5 |
2 |
97.5 |
11 |
Yes |
wheel weight |
12 |
Stick-on |
* |
** |
99.5 |
6 |
No |
wheel weight |
# 8 Magnum |
--- |
2-3% |
97-98 |
*** |
Yes |
Plumbers Lead |
--- |
--- |
****100 |
|
No |
Lead |
--- |
--- |
100 |
5 |
No |
*Not
known, presumably .5 to .75% tin. Stick-on weights are nearly
pure lead with a BHN of 6. |
**Not
known, presumably there is no Sb in stick-on weights. |
***#
8 Chilled Shot + 3% tin and cast into bullets tested 8 BHN. |
****Plumbers
lead should be nearly pure lead as is cable sheathing, lead
salvaged from X-ray rooms and roofing sheets. It may not be
pure enough for the purist front stuffers but it’s pretty soft
and valuable for alloying with the type metals. |
Salvaged lead
from sail boat ballasts could be and probably is almost anything. It would
be made up of anything each boat manufacturer could scrounge up and pour
into a mould to fit his hull. If you get a supply of this try casting a
few bullets with it (before adding it to alloy of known quality) to check
its castability and a few days later check its BHN so that you have a
better idea of what you have.
Salvaged range
lead can be quite the mix unless you’re familiar with the range and know
that a specific type of shooting is mostly done.
[1].22
lead is mostly lead, virtually no antimony, and usually about 1-2% tin.
Jacketed bullet alloy composition ranges anywhere from pure lead to 5%
Sb. As a very general statement, many handgun jacketed bullets have pure
lead cores (almost all Noslers, almost all FMJs, and most std. velocity
jacketed handgun bullets). Some have hardened cores (e.g. the Sierra 300
grain .44 Mag bullets is 5% Sb). If the range has centerfire rifle
bullets, then they are commonly 3% or 5% Sb. So the bottom line is that
jacketed bullets can contribute almost any hardness to bullet metal.
I have read reports of shotgun slugs being from near pure lead to
approximately 2-3% antimony. As with the sail boat ballast, check to see
how well it casts and check its BHN, checking the weight against bullets
from the same mould cast with a known alloy composition could help
identify the alloy, or at least narrow it down.
Before
blending any salvaged alloy with an alloy of known quality cast a few
bullets with it to assure that you don't have zinc or other contaminates
in the new alloy.
Salvaged battery lead should be avoided at all
costs. Since the advent of the maintenance free battery the
lead content has been reduced and elements such as strontium, calcium and
others have been added. Most of these elements cast very poorly, ruin a
pot of good alloy they are blended with and
are extremely toxic.
The quantity and quality of lead from
batteries is not worth the risk or the effort.
From
"Linstrum" on the
Castboolits forum
-
Maintenance free/low maintenance batteries use calcium metal-doped lead
to catalyze the hydrogen gas. The lead alloy used in batteries also
contains a bit of antimony and arsenic to help harden and strengthen the
lead. When hydrogen comes in contact with arsenic and antimony, the
hydrogen reacts to form ammonia analogues called arsine and stibine, AsH3
and SbH3. In World War One the Germans experimented with these as war
gases. As such they were highly effective since they are deadly in amounts
too small to easily detect.
Do
yourself and everyone else in the vicinity a favor and DO NOT use
batteries. Severe lung damage and even death could result. Sell the
batteries to a recycler and let the professionals deal with the risks.
Linotype:
(See type metal
composition chart below)
Linotype is the most common and
popular of the type metals used for bullet casting. At 84% lead, 12%
antimony and 4% tin, lino is a eutectic alloy meaning that it melts
and freezes at one temperature (464o) with no slushy
stage, just as single metals such as tin. With its percentages of
antimony and tin the fluidity of lino is exceptional and casts
perfectly filled out bullets.
An
advantage/disadvantage of lino is its 12% antimony. The advantage is in
taking advantage of its 12% antimony and using it to alloy with other lead
alloys. The disadvantage is that 12% antimony is a lot and produces very
brittle bullets. Bullets cast of straight lino are brittle enough that
they can be a poor choice for hunting bullets if any nose deformation is
desired or for use on heavy steel targets where it can and does shatter.
Monotype (19% Sb) bullets with only 7% more antimony are so brittle
dropping one on the floor or even simply chambering the round can actually
break it in two. The printing industry hasn’t used type metals in years
and it’s getting fairly difficult to find. If you’re going to cast of
straight linotype they are quite hard at 22 BHN and should be used with a
load that generates a minimum of 31,000 PSI to assure obturation.
Lino with its
eutectic 464o melting point can and should be cast at a lower
temperature than many alloys. The common practice of casting at 700o
to 750o or hotter is at least 236o over its liquidus
temperature. Dross formation and metal loss from oxidation can be reduced
by casting a little cooler, about 550o-600o. An
additional benefit of the reduced temperature is that the mould doesn’t
get as hot and you won’t have to wait as long for the alloy in the mould
to freeze, you can actually cast at a faster rate. When casting lino at
550o-600o be cautious of adding new alloy to the pot
too quickly and lowering the pot temperature below the liquidus and
causing dross to form or dropping the pot temp below liquidus temp..
(Newly
manufactured linotype made from virgin metals can be purchased
online from
Roto Metals, Inc) |
Wheel Weight Alloy:
[11]Metallurgically
or otherwise, there is no justifiable disadvantage to using wheel weights
for cast bullets. The wheel weight composition of 9% antimony in older
editions of the Lyman Reloading Handbook is very much out of date.
Recently obtained wheel weights average about 3% antimony.
There’s not much
doubt this is where the conventional wisdom comes from that wheel weight
alloy isn’t a good bullet alloy because the composition keeps changing. It
was changing 25-30 years ago, it has been reasonably stable since
then with minor changes from manufacturer to manufacturer as the
price of raw materials fluctuates. I
have used, heat treated and tested wheel weight alloy almost exclusively
for well over 15 years and haven’t found a difference significant enough
to effect the alloy ballistically. There can’t be any doubt that there are
minor differences from manufacturer to manufacturer and year to year
as the cost of raw materials fluctuates, but the simple truth is
that there hasn’t been a difference significant enough to affect
groups, velocity or final heat treated BHN during this 15 year period. My notes
indicate that the wheel weight alloy I have recently heat treated
achieved the same final BHN as bullets heat treated 15 years ago.
Pre-heat treated, as cast wheel weight alloy has fluctuated from 10 to 12 BHN during this time and my current
batch (about 500 pounds) is 11 BHN. Pre 1970’s wheel weights averaged 9%
antimony and during the 70’s this average was reduced, since the early
1980’s there appears to be little fluctuation in the percentage of antimony
in wheel weight alloy and currently seems to be about 3%, maybe, maybe ... 4%. Remember in the first paragraph I said consistency
in alloy from batch to batch is important? Wheel weight alloy has done
this for me for the last 15 years.
It's an
alloy that is readily available all across the country and anywhere from
free to fairly cheap. At 10-11 BHN air cooled with a couple percent of tin
added it is a good alloy for most non-magnum handgun loads and many light
to medium rifle loads. As an example, my 308 rifle shoots 11 BHN air
cooled wheel weight with 185 grain bullets at 1900 fps into surprising
groups at 100 and 150 yards with no leading. Wheel weight alloy is an
ideal bullet alloy for heat treating because of its percentage of antimony
and a trace of arsenic. This alloy can be heat treated to 30+ BHN. Most
loads do not generate nearly enough pressure to cause obturation at 30 BHN
and yes, obturation is a good thing. Very top end 454 Casull loads at
65,000 PSI should work well with 30 BHN bullets.
When
processing your wheel weights into ingots you should always separate the
clip-on weight from the stick-on weights (the ones with foam tape on the
back). Stick-on weights are nearly pure lead and by including them in your
alloy you are softening the entire batch by diluting the antimony content.
In addition, if your goal is to achieve consistency of your alloy, the
quantity and the size of stick-on weights in each batch will vary
considerably making
it impossible to duplicate the alloy the next time. Plus, it seems such a
waste of a good source of soft alloy.
More
and more wheel weight manufacturers are using zinc, steel, alloy and
even plastic
weights in place of lead. Zinc weights can be difficult to detect when
processing into ingots (some are painted to match tire rim color) and zinc
in your alloy will cause all sorts of casting problems. Wheel weight alloy
melting point is under 600oF and zinc melts at 787.15oF. When processing your weights into ingots keep the pot temperature at or
only a little above 650o and no hotter, the zinc weights will float before
they melt. If you see anything floating, remove it immediately.
An Additional
Consideration for Alloys:
In addition to
bullet base obturation additional considerations concerning alloy
strength and hardness in higher pressure/velocity rifle loads are
velocity, free-bore jump to the rifling and the rifling rate of
twist. The alloy must have the strength to make the free-bore jump
and take the rifling without stripping. A faster twist rate or
longer free-bore jump could possibly require a bit harder alloy;
cast bullets could suffer more from a longer free-bore jump and a
sharper twist rate than their jacketed counter parts. Additionally,
unsupported bullet noses (bore riders) can slump to one side under the stress of
acceleration; bullet design can play a role here as well as alloy
strength. It can be a balancing act that requires testing to
determine the minimum hardness (strength) of the alloy for these conditions
and yet not be too hard for that all important obturation.
Alloy Maintenance:
It’s not quite as simple as turning on the electric pot and pouring.
A basic knowledge of caring for your alloy is required and there are
a few tips that once understood makes this fairly simple. If these
rules are violated the percentages of metals and quality of the
alloy in your pot may not be what you thought it is.
[12]One
of the most critical yet least understood casting factors is temperature.
When a bullet caster refers to the melting temperature of the alloy, what
he means is the solidus or the temperature at which the alloy begins to
melt. More important is the liquidus temperature of the alloy, the point
at which the alloy is completely molten. An alloy may appear to be
completely melted in the pot when in actuality it is not, since crystal
formations of some of the important constituents of the alloy, such as tin
and lead or lead and antimony, still exist.
What this means for
the bullet caster is do not flux or add alloy (sprues, rejects or
new ingots) to the pot until the alloy has reached the liquidus
temperature. After adding alloy to the pot wait for the liquidus
temperature to be reached before fluxing. Every time metal is added to the
pot the alloy should be well fluxed. Once the liquidus temperature is
reached stir the melt before fluxing to assure even heat throughout the
melt. Add alloy to the pot slowly to aid in keeping the melt as close to
the liquidus temperature as possible.
[13]Dross
forms in a pot of molten metal by oxidation of the metal from exposure to
heat, air, impurities, and dirt, and from running the alloy below
its liquidus. As the metals melt, dross's (oxides of the metals) appear on
the surface of the molten metal. They must be returned to the melt by
fluxing, or else their removal as dross seriously depletes some of the
important constituents of the alloy.
Additionally, running the alloy too hot causes metal loss through
oxidation and more frequent fluxing to return dross to the melt.
Do not
allow the level of alloy in the pot to get below about half full so that
proper temperature can be maintained, the temperature of many electric pots will rise as the level of
alloy in the pot falls. Be cautious of the temperature falling below the liquidus point. Do not run the pot temperature any higher above its
liquidus temperature than necessary, about 50o - 75o F.
Solidus
and liquidus temperature. The solidus temperature is easy to determine (the alloy begins to melt)
but what is the liquidus temperature, the point where there are no
crystalline structures and all of the constituents of the alloy are
completely melted? To be honest I don't know, it would depend on the
metals in your alloy and the percentages of them. To play it safe my
practice has always been simply to wait until casting temperature is
reached before fluxing or adding alloy. I cast wheel weight alloy at 700o
and this is the temperature that I add alloy (even rejects or sprues) and
flux. Once I have fluxed I do not add anything to the pot through the
entire casting session, not even rejects or sprues. This is a simplified
method of how the metals industry maintains quality when blending alloys.
In the industry, metals are added to an alloy at a very specific
temperature that is based on the metal being added and the metals already
in the alloy. This would be quite an excessive degree to take bullet
casting, as long as metal is added and fluxing is done after
liquidus temperature (casting temperature) is reached we can maintain the
integrity of our alloy.
Key Points:
All of this might
sound complicated but in reality as bullet casters we don’t need to
be metallurgists but we do need an understanding of the basics. In
the above paragraphs you have learned what the basic metals and
bullet casting alloys are, some of their important characteristics
and how to care for them. Here is a review.
-
When accuracy, velocity or
expansion are
the prime concerns, consistency of the alloy from casting session to
casting session and batch to batch is important. Consistency of the
alloy BHN is important to both grouping and velocity extreme spread.
-
Too hard can be
worse than too soft. If your cast bullets are leading don’t
automatically assume the alloy is too soft, the problem could very well
be poor bullet fit or too hard of an alloy. Lead absorbs heat slowly and
it is extremely doubtful that bullet bases melt. Far more likely causes
of leading are bullet fit, lack of obturation, firearm dimensions or
lubrication.
Don’t blame the alloy for something that it didn’t cause.
-
Antimony hardens / strengthens lead. It helps the alloy flow and fill out the mould
with better, sharper detail. It is extremely brittle and if the bullet
is for other than paper punching the antimony should be held to about 6%
of the alloy. Antimony is what enables the heat treating of lead alloys.
-
Tin adds both
minor strength and minor hardening to bullet alloys. It reduces the
surface tension of the melt allowing the metal to flow and better
fill-out the fine details of the mould. Tin provides dross
protection up to about 750o. Tin reduces the melting point of
lead alloys plus the higher the percentage the more it limits the amount
of heat treating that’s possible. Higher percentages of tin cause faster
age softening.
-
Arsenic is a
"catalyst" in lead/antimony alloys enabling hardening
(strengthening) by heat treatment
far above what the percentage of antimony would suggest. Only a trace is
needed and adding more will not further harden the alloy. Arsenic itself
adds very little to the hardness of lead alloys. Wheel weights, chilled
shot and magnum shot are excellent sources of arsenical lead alloys for
the bullet caster to enrich his antimony alloy for quenching or heat treating.
-
The type metals
are an excellent source of antimony and tin (but not of arsenic) for
alloying with soft salvaged lead alloys and an unlimited variety of
different alloys can be made.
-
Clip-on wheel weights and stick-on
weights should be separated when processing wheel weight into ingots.
Clip-on wheel weights are an excellent bullet casting alloy with its
percentages of lead/antimony and arsenic. 2% tin can be added for better
dross control and thus mould fill out. This alloy runs 10-11 BHN air
cooled and can be heat treated to 30+ BHN. Proper fitting bullets of 11
BHN in a properly dimensioned firearm are adequate for all but magnum
handgun loads, water
quenching or heat treating wheel
weight alloy will easily extend its use to magnum handgun loads and
mid-range rifle loads. When processing
wheel weights into ingots the melt temperature should not be much over
650o and keep a watchful eye for zinc weights.
|
Stick-on WW,
45 ACP 200 gr. HP @ 800-850 fps fired into water. |
|
-
Stick-on wheel
weights are an excellent source of very soft alloy (about 6 BHN). This
alloy makes very effective HP bullets for light and medium pressure 45
ACP loads and expansion is dramatic. It is fairly close to a pure lead
and can be used to alloy with the type metals.
-
The alloy should
never be fluxed or metal added until it reaches its liquidus (casting
temperature.) After alloy is added wait for the temperature to return to
its liquidus before fluxing. Don’t skim off the metal oxides,
flux them back in. Keep the alloy well fluxed. Don’t run the pot
temperature any higher above its liquidus than necessary (about 50o
F is fine) to keep oxidation to a minimum. A tip on reducing oxidation
of the melt, using a flux that doesn’t burn off (such as sawdust) and leaving it on top of the melt after fluxing and while
bottom pour
casting and will help keep air off the surface and reduce oxidation. Try
and avoid air flow (an electric fan for example) across the top of the
melt.
-
It should be
obvious by now that a critical piece of casting equipment for
maintaining consistent alloy from batch to batch, maintaining the
integrity of the alloy and casting bullets of consistent, repeatable
quality is a quality lead thermometer.
|
Top of Page |
Alloy Recipes |
See also this recipe article:
Alloying Antimony
With Roto Metals Super Hard |
|
Formulas using
magnum shot Computed @ 4% Antimony and 1½% arsenic |
Formulas using
stick-on WW computed as straight lead |
Formulas using
clip-on WW Computed @ 3% Antimony and .5% tin |
|
|
|
Clip-on
wheel weights - 20
pounds |
|
Monotype
- 2 pounds |
Stick-on
wheel weights 15
pounds |
Linotype
- 3 pounds |
Clip-on Wheel
weights - 4 pounds |
Lino
5 pounds |
Clip-on Wheel
weights - 9 pounds |
lead - 3
pounds |
Lead
Shot - 4
ounces Tin
- 9.6 ounces |
Tin |
Antimony |
Lead |
Tin |
Antimony |
Lead |
Tin |
Antimony |
Arsenic |
Lead |
1.4% |
4% |
94.6% |
2.2% |
5.25% |
91.9% |
3% |
4% |
.25% |
92.75 % |
Add 1% tin.
|
Good Magnum alloy |
Quench/oven
HT to 18 - 30+ BHN |
|
|
|
|
|
Clip-on
wheel weights - 20
pounds |
Linotype
- 5 pounds |
Linotype
- 2 pounds |
Tin
- 6.4 Ounces @ 2% |
Clip-on Wheel
weights - 5 pounds |
Clip-on Wheel
weights - 5 pounds |
or 9.6 Ounce
@ 3% |
Tin |
Antimony |
Lead |
Tin |
Antimony |
Lead |
Tin |
Antimony |
Arsenic |
Lead |
2.25% |
7.5% |
90.25% |
1.5% |
6.3% |
92.2% |
2 1/4% |
4% |
1/4% |
93 1/2% |
Approximate
Hardball BHN |
Nearly Lyman # 2
BHN |
Oven heat
treats to 30 - 34 BHN |
|
|
|
|
Monotype
- 3 pounds |
|
Linotype
- 4 pounds |
Clip-on Wheel
weights - 4 pounds |
Clip-on
Wheel Weights
- 9 pounds |
Clip-on Wheel
weights - 6 pounds |
lead - 3
pounds |
50/50
bar solder - 1
pound |
Tin |
Antimony |
Lead |
Tin |
Antimony |
Lead |
Tin |
Antimony |
Lead |
1.9% |
6.6% |
91.5% |
3% |
7.2% |
89.8% |
5% |
3% |
92% |
Approximate
Hardball BHN |
Medium hard
alloy. Magnum handgun & rifles to 2,000 fps |
Close to Lyman #
2 Alloy |
|
|
Clip-on Wheel
weights - 10 pounds |
Clip-on Wheel
weights - 9 pounds |
Clip-on Wheel
weights - 10 pounds |
Stick-on
Wheel Weights - 4 pounds |
Linotype
- 2 pounds |
Stick-on
Wheel Weights - 4 pounds |
Virgin bar tin - 4
ounces |
Virgin bar tin - 7
ounces |
Tin |
Antimony |
Lead |
Tin |
Antimony |
Lead |
Tin |
Antimony |
Lead |
.35% |
2.2% |
97.65% |
2.1% |
2.1% |
95.8% |
4.9% |
4.45% |
90.65% |
Trace of Arsenic -
About 7 BHN |
Trace of Arsenic -
About 7-8 BHN |
Lyman # 2 Alloy
duplicate |
|
|
|
NOTE: Not
all alloy recipes listed above were tested by the author. |
Super Hard, custom alloys or pure alloys can be
ordered to your specifications from
Roto Metals, Inc. w/free
shipping on many orders. |
|
Top of Page |
|
Formulas using
additional tin used 99.9% pure bar tin unless noted |
|