Effects of age hardening on our cast bullets

[kelbro]

Exactly how does age hardening affect our bullets? I understand they get harder with time but what does that really do to/for us?

If you have a load worked up with a bullet that has been aged 2 weeks, is it going to change POI if you load it after 6 months? After 1 year?

How about if you load it after 2 weeks and wait 6 months or 1 year to shoot it?

Is it more or less likely to lead your barrel (providing fit and lube are optimum)?

[Ricochet]

If you're talking about air cooled boolits, they won't age harden enough that you'll notice a difference in how they shoot.

[Bret4207]

AC boolits might gain 2-3 points over 2 weeks time, 4 at the outside IME. It depends on the alloy. What that might do for you depends on your gun and load and where the perfect balance point is. In many cases it won't make enough diff to notice, other times it'll make all the diff, but at those small levels it's probably rare. The softening occurs over decades-allegedly.

[kelbro]

Thanks. That's what I was thinking but never considered it until I started reading some of the posts here.

[Shiloh]

Others here have suggested that they harden for about 2 weeks.Water dropped that is.
I have to agree. I have noticed a continuance of the hardening by applying the thumbnail scratch test.

Shiloh

[Dale53]

I have a hardness tester. Antimonial alloys WILL harden after casting. Most of the hardening takes place in two weeks.

Dale53

[geargnasher]

I have a hardness tester. Antimonial alloys WILL harden after casting. Most of the hardening takes place in two weeks.

Dale53

+1 Dale. Like Bret said, 3-4 points over a couple of weeks for AC WW-type alloys. I've checked this many times with batches to get an idea of how long to wait before shooting, and short of graphing daily test results over time I can say that after a week the difference is practically nil for all but the most demanding applications.

It is my understanding that Arsenic aids in speeding up the hardening process (especially after heat treating or water-dropping) but I have no way to know what the arsenic content of my alloys are to do a comparison.

Gear

[montana_charlie]

Part of the results obtained by Dan Theodore during a 28-week test of 'age hardening/softening' in air-cooled alloys.

http://castboolits.gunloads.com/picture.php?albumid=88&pictureid=1530

These are for some of the antimonal alloys he tested.
The rest of his findings have not been published, yet.
CM

[runfiverun]

that sure makes a good case for not using more tin than antimony right there.

[243winxb]

Good reading here. http://www.castpics.net/memberarticles/arsenic.htm And another i have saved.
Lead is normally considered to be unresponsive to heat treatment. Yet, some means of strengthening lead and lead alloys may be required for certain applications. Lead alloys for battery components, for example, can benefit from improved creep resistance in order to retain dimensional tolerances for the full service life. Battery grids also require improved hardness to withstand industrial handling.

The absolute melting point of lead is 327.4°C (621.3°F). Therefore, in applications in which lead is used, recovery and recrystallization processes and creep properties have great significance. Attempts to strengthen the metal by reducing the grain size or by cold working (strain hardening) have proved unsuccessful. Lead-tin alloys, for example, may recrystailize immediately and completely at room temperature. Lead-silver alloys respond in the same manner within two weeks.

Transformations that are induced in steel by heat treatment do not occur in lead alloys, and strengthening by ordering phenomena, such as in the formation of lattice superstructures, has no practical significance.

Despite these obstacles, however, attempts to strengthen lead have had some success.


Solid-Solution Hardening

In solid-solution hardening of lead alloys, the rate of increase in hardness generally improves as the difference between the atomic radius of the solute and the atomic radius of lead increases.
Specifically, in one study of possible binary lead alloys it was found that the following elements, in the order listed, provided successively greater amounts of solid-solution hardening: thallium, bismuth, tin, cadmium, antimony, lithium, arsenic, calcium, zinc, copper, and barium.

Unfortunately, these elements have successively decreasing solid-solution solubilities, and therefore the most potent solutes have the most limited solid-solution hardening effects. Within the midrange of this series, however, are elements that, when alloyed with lead, produce useful strengthening.

A useful level of strengthening normally requires solute additions in excess of the room-temperature solubility limit. In most lead alloys, homogenization and rapid cooling result in a breakdown of the supersaturated solution during storage. Although this breakdown produces coarse structures in certain alloys (lead-tin alloys, for example), it produces fine structures in others (such as lead-antimony alloys). In alloys of the lead-tin system, the initial hardening produced by alloying is quickly followed by softening as the coarse structure is formed.

At suitable solute concentrations in lead-antimony alloys, the structure may remain single phase with hardening by Guinier-Preston (GP) zones formed during aging. At higher concentrations, and in certain other systems, aging may produce precipitation hardening as discrete second-phase particles are formed.

Alloys that exhibit precipitation hardening typically are less susceptible to over aging and therefore are more stable with time than alloys hardened by GP zones. Lead-calcium and lead-strontium alloys have been observed to age harden through discontinuous precipitation of a second phase Pb-Ca and Pb-Sr in lead-strontium alloys as grain boundaries move through the structure.


Solution Treating and Aging

Adding sufficient quantities of antimony to produce hypoeutectic lead-antimony alloys can attain useful strengthening of lead. Small amounts of arsenic have particularly strong effects on the age-hardening response of such alloys, and solution treating and rapid quenching prior to aging enhance these effects.
Hardness Stability. For most of the two-year period, the solution-treated specimens were harder than the quench-east specimens. Other investigations have also shown that alloys cooled slowly after casting are always softer than quenched alloys. The alloys with 2 and 4% Sb harden comparatively slowly, and the alloy containing 6% Sb appears to undergo optimum hardening.

Application. Because of the detrimental effect of antimony on charge retention, the effort to reduce antimony contents of the positive plates in lead-acid storage batteries has led to the trend of replacing eutectic alloys with a Pb-6Sb-0.15As alloy. Battery grids made of this arsenical alloy will age harden slowly after casting and air-cooling. However, storing grids for several days constitutes unproductive use of floor space and results in undesirable interruptions in manufacturing sequences.

Although large-scale solution treatment of battery grids might be difficult to justify economically or to achieve without some distortion, quenching of grids cast from arsenical lead-antimony alloys offers an attractive alternative method of effecting improvements in strength. The suitability of quenched grids can be assessed by comparing with the hardness level that battery grids require in order to withstand industrial handling (about 18 HV, the hardness of the eutectic alloy). The alloy containing 2% Sb clearly does not respond sufficiently to be considered as a possible alternative. The 4% Sb alloy, however, attains a hardness of 18 HV after 30 min, and the alloys that contain 6, 8, and 10% Sb could be handled almost immediately.


Dispersion Hardening

Another mechanism for strengthening of lead alloys involves elements that have low solubilities in solid lead, such as copper and nickel. Alloys that contain these elements can be processed so that no homogenization results; most of the strengthening that occurs is developed through dispersion hardening, with some solid-solution hardening taking place as a secondary effect.
The resulting structure is more stable than those developed by other hardening processes. Dispersion strengthening also has been achieved through powder metallurgy methods in which lead oxide, alumina, or similar materials are dispersed in pure lead.

[John Boy]

Boy Oh Boy ... how did I miss this thread?
Charlie and 243 ... thanks for the empirical data! Saved it quickly to my computer.

I finished casting 100 Mini Grooves today, 530gr nominal, 1:20 alloy. Started weighing the lot while they were luke cold and warm. Then reweighed some that were 530.0 to 530.5 ... the weights got a few tenth's heavier. So, thought wave ... where is some empirical data for max time period Bhn and weight of lead? Did a search on the forum and up pops the exact data I was looking for ... Thanks. You both made my day!:D

A Very Enjoyable Thanksgiving to All

[KYCaster]

Hmmmm....I understand how hardness and size can change with time, but I don't understand how weight can change.

Jerry

[Ricochet]

Depends on whether you're talking about the boolits or the booliteer.

[JonB_in_Glencoe]

This is a great chart.

Part of the results obtained by Dan Theodore during a 28-week test of 'age hardening/softening' in air-cooled alloys.

http://castboolits.gunloads.com/picture.php?albumid=88&pictureid=1530

These are for some of the antimonal alloys he tested.
The rest of his findings have not been published, yet.
CM

[gwpercle]

The only time I ever noticed that age hardening was going on was once after casting some boolits , 9mm RN , 50-50 COWW-range scrap , I sized a bunch the next morning from .358" to .357" , I had a flat nose punch in the sizer but didn't change it to RN ...in a hurry , They were easy to size and the nose punch left a little flat spot on the boolit , 1/8 " dia. meplate at most . A week later the rest of the boolits sized with hardly any flat on the RN and were a little harder to size from .358" to .357".
No change in impact or POI was noticed ... but this was handgun ammo at hangun ranges.
I would have never noticed the difference if I hadn't needed a few sized boolits to complete a box of reloads .
They do size down easier when soft... that is true !
Gary

[Don1357]

The practicality of hardening often boils down to 'it doesn't matter' because most likely than not by the time they hit the range enough time has passed that the 'hardness' is baked into the equation.

Meaning: You work up an alloy, eventually load bullets with the boolits, take it to the range, and maybe wonder if going a tad softer would work better. So you cast new boolits with a tad more pure lead, eventually load bullets, eventually take them to the range, and either it helped or it didn't. What you often don't think about is that from casting to 'Honey! I'm going to the range!" it took enough time that all your batches of boolits had a chance to reach its final harness.

All we can do is cast and test to see if the alloy is suitable. Age hardening is often a distraction. If the boolit ended up too hard make it softer.