Discussion in 'Reloading Forum (All Calibers)' started by Webster, Aug 6, 2019.
Got some fact to it, Not bad.
I doubt they know what we care about. Their interest is in manufacturing brass, not optimizing the hardness for benchrest grade accuracy. I'm sure they've got a grip on process and how to get it where *they* want it, though.
Oh I think cartridge case manufacturers know exactly what's desirable as do manufacturers of machines for exactly this purpose. https://radyne.com/products/small-caliber-ammunition-annealing/. You can't optimize a process for benchrest when you don't even understand fully what's going on.
Read the Report 1231/1A on the AMPS website. It explains eveything you need to know. If you cannot understand it it's your problem.
One of many I’ve read on the topic, nothing new there for me...
Or maybe they know what a can of worms they would open.
There is this. One that the mouth per se is not included just up to 1-1/2” from the head, which on a 308 is the base of the shoulder. The “anneal” has no grain size requirement, likely because it will be different depending on the process used and the starting grain size.
What we're doing is most definitely annealing. There's three phases to annealing, recovery, recrystalization, and grain growth. What we're doing (attempting to do), is recovery annealing. That is, applying enough heat energy for sufficient time to allow the rows of dislocated atoms to rearrange themselves into a lower energy state without applying so much heat as to change the grain structure of the material. "Full annealing" refers to heating the material beyond the recovery phase into recrystalization and grain growth where the grain structure is changed. In school the textbooks we used referred to it as Partial and Full annealing but I think Recovery annealing is a better term because it matches the recovery phase of annealing.
Found this as I was doing some light research...
Metals are cold worked in order to change their shape. A material loses ductility when it is cold worked or moreover, cold rolled. If one wishes to partially or fully restore a cold worked material to its original properties, one can anneal the material. Annealing is performed by heating a material; in this instance, the material is a metal. There are three stages of annealing and each stage produces different results. The three stages of annealing are recovery, recrystallization, and grain growth.
The recovery stage is the first stage of annealing. This stage occurs when the metal is first subjected to heat. The dislocation density and grain distortion in the material is little affected by this stage of annealing. However, the recovery stage eliminates most of the residual stresses in the material. One can think of this as the heat relaxing the built up tension in the material. Much electrical conductivity is restored in the material as well. The recovery stage permits the dislocations to move slightly and form what is known as the polygonized subgrain structure.
As a cold worked material is subjected to a temperature at or above its recrystallization temperature, new grains begin to nucleate from the cell boundaries created by the polygonized subgrain structure. This nucleation eliminates most of the dislocations in the worked material.
As the subjected temperature is raised higher, the grains grow and a fine recrystallized grain structure is produced. The larger, faster growing grains consume the smaller grains in the process. All of the effects of cold working are eliminated at this point. Grain growth can be detrimental to the properties of the material and can typically produce a rough surface appearance on components formed from sheet metal.
Time and Temperature
It is found that temperature variations have a much stronger influence on the annealing of metals than time variations. The standard annealing time is one hour; only temperature is varied. The annealing temperature is dependent on the component’s thickness, composition, and geometry.
Annealing Temperature and Activation Energy
The minimum annealing temperature for an actual effect to be had from annealing is approximately one-third to one-half the melting point of the material specimen. Because there is a minimum temperature, the annealing process is governed by an Arrhenius Rate Equation. Because it is difficult to measure recrystallization, the 50% recrystallization time is measured as the time at which the metal reaches half its original hardness.
Amazing, the information just pops out of nowhere when you guys use the correct terminology instead of making stuff up
Even that is for manufacturing, not the tea leaves of trying to shrink a group by 1" at 1000 yards.
Our annealing has recrystallization and grain growth can be seen if annealing a really worked piece of brass if annealed correctly. AMP goes into recrystallization in their “Annealing under the microscope” articles.
My point is simply that if you don’t understand the metallurgy etc in even basic detail - let alone intricate detail - you aren’t in a position to refine anything for a narrower, more precise purpose. I’ve read many threads here on annealing. What is clear is that the general level of knowledge is actually rather low. I’ve yet to read a clear description with a precise understanding of what is done at manufacturing and the impact on the brass then let alone refining that further. There’s a lot of guessing. I built a fairly sophisticated version of the GinaErick induction annealer. Painting brass cases with Tempilaq is still guessing at required times let alone providing an understanding of whether the brass has been changed appropriately, over the appropriate area, at a molecular level.
No doubt we have a poor grasp of what happens to the brass, mostly because it's too expensive for most of us to test. But I would go a step further and say that for accuracy purposes, we don't even know what we want the brass to look like after its annealed. AMP seems to assume that restoring it to a factory new condition is the goal. I have no idea why they think that. It seems totally arbitrary. I'm not even sure that there is one perfect state. I bet it depends on multiple factors.
For case forming or reducing split necks, sure. That's easy - make it soft.
I’m annealing after firing using an Annealeez and 750 deg tempilaq because I read somewhere that annealing can have a positive affect on consistent neck tension and down range results. Having no way to know what’s going on at the molecular level I take much of this based on faith.
How do we determine whether this practice is worth the time and effort in some empirical fashion? Otherwise, this is just an esoteric discussion on the vagaries of metallurgy
Let me provide some more uncertainty. Last year I came back to LR BR and started annealing after every firing because I thought AMP annealing put the case back to its unfired state. Then I heard that when cases are hardness tested, the Brinnel hardness of annealed cases is erratic and makes them less consistent than if they are left un-annealed.
So last year everything was annealed. This year one set of cases was annealed once, and another set of cases not annealed at all. There has been no significant difference in seating consistency or group size for these three scenarios.
Then there is the additional consideration that if you aren't bringing the brass completely back to the ground state every time it is fired, some of the effects are likely cumulative.
The link provided by jthor above to "Recrystallization Behavior of 70/30 Brass", was a very good read. It appears to be part of a Thesis, and a number of considerations occurred to me while reading it. The short version is that we may or may not be fully supporting the grain growth phase during the typical cartridge brass annealing process, but we are most definitely supporting recovery and recrystallization.
To that end, the work did not directly address some of the questions and concerns we have as reloaders. Specifically, are we annealing sufficiently that there is minimal cumulative "carryover" of the cold work effects through multiple firings? Second, what is the minimum time requirement at a specific temperature to ensure this is so? I've looked through a number of papers/studies aimed at the brass annealing process, and they're generally carried out with a different goal in mind than ours. Specifically, the annealing times used in these studies are generally far longer than we could ever get away with because we have to limit the annealing process to the neck/shoulder region. Annealing for time periods in the minutes to hours range would dramatically increase the risk of impairing the structural integrity of the case wall and case head regions via conduction. So we generally limit our annealing times to the range of a few seconds or so.
FWIW - I use a Giraud [torch] annealer and have always use a flame/time setting that heats the case necks up to a very dull red color as observed in a fully darkened room. The duration of the anneal is typically about 10-12 seconds for a .223 Rem case, and about 16-18 seconds for a .308 Win case. Based on relatively crude estimates of temperature from the color of the glow, I would conclude that the temperature of the brass was likely to be in at least the 750 - 850 degrees F range, possibly even a tick higher. Based on the information provided in the link jthor provided and elsewhere, this should be more than sufficient to anneal the brass.
The question then becomes, am I grossly over-annealing the brass? It is an issue over which I have always been concerned. Nonetheless, I can state with certainty that I have used the exact same process for years, through many different Lots of brass, through many firings, and I have never yet experienced any issues with brass exhibiting behavior that would indicate excessive annealing. In contrast, I have read a number of reports about the annealing process which seem to indicate that the effects of cold-working brass via firing may not be completely reversed by annealing when an insufficient time and/or temperature is employed, and can then be carried over and accumulate with multiple firings. To that end, I believe heating the brass to a dull red color in a darkened room, although a crude and not very scientific approach, is essentially one which pushes the annealing process to the maximum extent we can realistically achieve without softening up the cases in places that are not desirable.
Fair enough, I was just explaining the science behind it. It doesn't matter to me if they have a different opinion of what constitutes "correctly annealed", that's something for the board to fight about, I don't have a horse in that race. The science is still the same regardless of how shooters decide to go about it.
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