6.5x53.5 SR Daudetaeu

Hi all

Just doing some inspection on a lot of Daudetaeu N12 (6.5x53.5 SR). As it is well known, this cartridge has a design and/or manufacturing defect that causes longitudinal cracks on the case neck. Then the oxygen and humidity trigger the corrosion mechanisms to end up in this disaster:


After doing more inspection on the units (more than 40 units) I have come up with:
* The head stamped units DAUDETAUE N12 (Keller & Co. 1893 - Austria) have a circular shaped powder:

Some comments and questions:

  1. From 10 “G de U” units, 9 had the rectangular powder but just one bears the circular style powder as the Australian unit. These units was dated 1896 and does not look to be re-loaded units.
  2. All the SFM (about 10) have the rectangular powder
  3. The manufacturing defect that could generate the neck cracks is the annealed. It is a thermal process to relieve stress or tension on the metal after stamping. A bad annealing or not performing this process can be the root cause of this well known defect. However, the annealing is a thermal process that combines temperature and time, something that is set for each lot and each manufacturer can have different settings. In any case we can see the same defect on the cases form Keller and SFM, also the same defect for cases made in different years. My suspicion is that the root cause is multi-cause and not only linked to the annealing. Thoughts?
  4. it looks like two stamping die of the headstamp G de U 1896 were used, there are small differences. This was new for me.

Saludos
Daniel

Yes lack of case anneal is the case of the neck crack, Different metals expand & contract differently & forces are exerted. Just like bending a piece of plastic or tin it will eventually split.

i also believe that the early smokeless powder is deteriorating and the nitric acid in it may be helping the process along.

Daniel, what you and Pete concluded is right on the money. I can add some history and the science behind it. I’m going by memory on some of this, so hopefully I have it right.

Unfortunately, this problem was not well known when your cartridges were made.

The British first discovered cracked necks in India in the late 1800’s during the monsoon season (and named it “Season Cracking”). But the cause was not known until after WW1. Sometime between those two periods annealing was found to solve the problem, even before anyone knew why. Because your cartridges were made prior to 1900, there is a good chance they were not annealed (because they just didn’t know at the time).

After the problem was understood, it became known as “Stress Corrosion Cracking” and now just “Environmental Cracking.” This will only occur if all three conditions are met: 1) high enough stress, 2) a susceptible alloy and 3) certain chemical environments. Remove only one condition and no cracks will occur, so this is your multi-cause.

One thing most cartridges have in common is the alloy, cartridge brass. Unfortunately, cartridge brass is highly susceptible to Environmental Cracking. But it is also easy to fix (when the ammo is made) if you know the root cause.

The British cracks were caused by work-hardened necks (stress form forming) and being exposed to urine in horse stables. The ammonia from the urine combined with moisture in the air, along with high stress, caused the cracks.

Stress in a cartridge case will be highest in the neck and especially at the mouth. If you look at a draw set, you can see that a case starts out as a flat slug and gets progressively longer as it takes shape. So the neck is worked more than the walls because it is further from the original slug that makes up the base. More cold work = more residual stress.

Annealing reduces the stress (how much depends on time and temperature as you said). Reduce the stress enough and the other two factors (alloy and environment) won’t be a problem.

More recently other chemical were found to cause it, such as nitric acid (from the unstable powder as Pete said) and also mercury compounds (primers). So even if you don’t store your cartridge collection in a barn, the powder and/or primer can cause cracks in cases that aren’t annealed. Better powder processes and different priming compounds made a difference, so not all old cartridges will crack (or at least not disintegrate).

The cup shaped granules are characteristic of Austrian rifle propellant in the period from the 1890s until the end (I think) of World War I. Flake (square biscuits) powder was near universal in French and German rifle propellant for decades and much used elsewhere. Jack