Does Necking Down Brass Affect Neck Tension?
Recently a customer reached out with pressure concerns in Starline 6mm Creedmoor brass that had been formed from Starline 6.5 Creedmoor cases. The brass had been fired twice and some cases would no longer hold the primer. As this is an uncommon issue, the customer was asked to supply his load data so I could do some further examination into what could be causing the shortened case life.
At first, the problem seemed pretty cut and dry. I quickly discovered the load was at maximum in Hornady brass, according to their published reloading data. Starline brass has a lower case capacity than Hornady brass due to Starline’s increased thickness at the base, so I knew this was probably most of the problem. We always recommend that customers start on the low end of load data and carefully work their way up when changing brass manufacturers as not to run into pressure problems.
Knowing that working brass makes it harder, I suspected neck tension played a role in raising pressures as well. A case that is neck annealed and then formed into a smaller caliber would be harder than a case that is formed into the smaller caliber and then neck annealed. To prove this, I took a sample of Starline 6mm Creedmoor, 6.5 Creedmoor, and 6.5 Creedmoor formed into 6mm and crushed the necks in a jig at a pre-determined load and compared them. The test quickly showed how hard the neck is, and a direct correlation to neck tension with everything else being equal. The picture below shows just how much harder the necks are on the 6mm Creedmoor necked down from 6.5 Creedmoor cases.
Neck annealing is a heat treatment that softens the neck of the case to increase its ductility and give more consistent bullet tension. Even with just a .021” reduction from .264” down to .243” caliber, the test proves neck annealing would be a good idea. Annealing will not only make the case last longer, but will reduce the excessive neck tension on conversions such as this.
If you have any questions or concerns with Starline brass, we encourage you to reach out to us at firstname.lastname@example.org or give us a call at 800-280-6660. We’ll be happy to help.
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