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
There's some great information in the articles on the AMP website that provides a lot of evidence for issues on annealing:
https://www.ampannealing.com/articles/
There were a lot of highlights I made that interested me and maybe you and other's here (a bit many, and my just highlights, taken from their reports at the above link):
as the carbon layer increased (microscopically), the force to draw the bullet
decreased. It would appear the carbon acted as a lubricant. Interestingly, the standard deviation also improved i.e. the case to case variation in the force required to draw the bullets decreased”
4 hours of SS tumbling
hardens the surface of the case wall by 15 – 25 HV. When the same case is sectioned however, the cross section of the case wall can be tested (see photo above right). This showed that
no work hardening occurs deeper into the cross section. The tumbling effectively creates a harder "skin” on the surface which is undetectable even under 200X magnification or higher
neck and shoulder regions of cases must be "flash annealed” so that the heating is localised. This requires a higher temperature over a shorter time
The greater the hardness, the greater the force needed to draw the bullet for a given interference fit. The packs highlighted in yellow were sized with a fairly aggressive neck die with expander ball. That hardens the neck considerably more than the bushing die without expander, and
greatly increases the force needed to draw the bullet.
carbon was removed from inside the necks. This made a dramatic improvement to the batch to batch consistency
as carbon built up inside the necks, the average tensile force progressively
decreased from 103 lbf for once shot cases (Pack 3) down to 74 lbf for three times shot (Pack 4), and just 43.5 lbf for ten times shot cases (Pack 5)
appears that graphite does not coat
freshly annealed brass as thoroughly as either unannealed brass, or brass that has been annealed and set aside for a day or two. We did experience some galling where dry (graphite) lube was used, in particular with pack 1.
Not surprisingly, the results clearly show better results using a bushing die (packs 3, 4 and 5) compared to a standard neck die with expander ball
The bushing die used in this set of tensile bullet pull tests gave significantly more consistent results than the standard neck die with expander ball.
Cases should be annealed every reload in order to get the best repeatability.
The effect of case weight variations on annealing is more significant in some brands than
others. If weight variations are
only located in the case heads, then annealing is unaffected. If a portion of the variation is in the neck and shoulder, then annealing results will vary. Premium brands such as Lapua, Peterson and Norma tend to have small spreads of weight across any given lot. What weight variations
do exist tend to be located in the case head, where it doesn’t affect annealing. In other brands tested in this study there is a
direct correlation between case weight and annealing results, indicating that at least part of the weight variation in those brands is in the
neck and shoulder region.
It is only after cases have been sized at least once that consistent annealed neck hardness will be achieved reload to reload. This is due to the level of "stored energy” which sizing creates. Therefore, reloaders should either: directly load virgin cases and not anneal until the
second reloading cycle,
or simply run virgin cases through a neck die with expander before starting the first load. This will pre-harden the cases sufficiently to ensure the first and every subsequent anneal gives repeatable results
Note that both cases had been lightly neck turned to remove high spots. After turning, both still showed neck wall variations from 0.013” to 0.014”.
as with Lapua, showed
no correlation to case weight. Comparing these results to "B and "C” tests, firstly, the case weight variations are much lower in Norma and Lapua. Secondly,
what variation there is does not appear to be in the neck and shoulder region. It is therefore more likely to be in the head of the cases.
The Peterson cases showed
no correlation between weight variability and either AZTEC code generation or annealed hardness, and therefore, as with Norma and Lapua, we conclude that there is no significant weight variation in the targetted neck and shoulder region. They showed excellent consistency.
Does variable case weight result in variable annealing hardness? -
That depends on the
cases. With all three brands "A”, "B” and "C”, we saw a considerable increase in annealedhardness as case weight increased. The Lapua, Peterson and Norma cases showed no such trend.
Neck wall thicknesses should be checked before even starting to weigh cases. Each 0.001” will make a significant difference, as can be seen in our Standard program listings
