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          Does tightening the neck of the cartridge case to smaller diameter affect tension on the bullet?

           Michal Štrobl ml.  Michal Štrobl ml.
          Michal Štrobl ml. 
          04.04.2022
          A customer contacted the manufacturer of Starline Brass cartridges with concerns about the pressure in Starline 6mm Creedmoor cartridges, which were created from Starline 6.5 Creedmoor cartridges.

          The brass had been fired twice, yet some of the cartridges no longer held the primer. As this was an unusual problem, the customer was asked to supply laboratory data so that further investigation could be carried out to determine what might be causing the reduced life of the cartridges.
           
          Initially, the problem seemed quite clear. The customer was using the highest load according to the Hornady tables. Starline cartridges have a lower internal case capacity than Hornady cartridges, which is due to the greater strength of the material at the bottom of the case, so it was a safe assumption that this was probably the majority of the problem. We always recommend that reloaders start at the bottom load in their load table and work their way up carefully, so they don't run into pressure problems.
           
          Since the neck retraction makes the cartridge case harder, it was suspected that neck tension plays a role in increasing the pressures in the case. A cartridge case that has the neck annealed and then formed to a smaller caliber would be harder than a cartridge case that is formed to a smaller caliber and then annealed at the neck. For a practical check, samples of Starline 6 mm Creedmoor, 6.5 Creedmoor, and 6.5 Creedmoor cartridge cases formed to 6 mm caliber were compared. The necks of these cartridges were subjected to the same hardness test by a calibrated impact on the outside of the neck. The test quickly showed how hard the neck was and a direct correlation to neck tightening, all other conditions being equal.
           
          Neck annealing is a heat treatment that softens the neck of a cartridge case to increase its extensibility and achieve a more consistent tension on the bullet. Even with just a .264" reduction of .021" to .243", the test showed that neck annealing would be a good idea. Annealing will not only extend the life of the cartridge case, but will also reduce excessive neck tension on conversions like this.

           

          Source: https://www.starlinebrass.com/

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