How Case Neck Tension Affects Performance?

Determining the proper neck tension or case neck tension is something that we’ve heard a lot about but have seen very little data that helps us reloaders understand what we want to know. Reloaders tend to use a lot of words that don’t necessarily mean anything to a website but yet they mean something to us. However, these kinds of things can often vary from person to person. A common definition of neck tension is the actual amount of force required to seat a projectile into or pull out of a case. You might use something like an arbor press with a force pack to monitor this value as you see projectiles. Many people define this term as the difference between the projectile’s diameter and the inside diameter of the neck after the sizing operation is complete. So if you’re working with the 308 projectile and inside case neck measure is 306. 

In this article, we are going to cover up how case neck tension affects your reloading performance and explore four different ways to set case neck tension neutral. So let’s get started…

1. Using a Standard Full-Length Die

A standard full-length die is going to oversize the neck of a case so when the expander ball is pulled back through the neck of the case. The case neck tension is a function of the size of the expander ball used to resize the case neck. Standard full-length dies work this way because case neck thickness can vary by manufacturer, lot, or probably other factors. Oversizing the neck of the case and then running the expander ball ensures that. Every different manufacturer’s case and every single lot should at least function for any combination.

2. Full-length Dies

Some manufacturers have a honing service. You can have the neck portion of the die opened up to whatever diameter just as if you were using a bushing die. The downside of this is if you end up wishing that you could change its diameter once one and done. Switching brands of brass case, neck wall thickness or possibly even lot variation could cause an issue in your reloading Hornady Load Data process but it is optional.

3. Use of Bushing Die

Many manufacturers have bushing dies and use bushings sold in 1000 increments to set this neck tension value. One of the negative things often overlooked for this type of method is any difference in case wall thickness variation can cause uneven pressure on varying sides of the projectile. Maybe this does or doesn’t affect reloads but it’s something to consider. Switching brands of brass possibly might change the value of bushing that you need so you might need more than one on hand. Bushings aren’t an extreme cost when it comes to the entire reloading process. If you don’t know what value you need out of the gate you’re probably gonna end up getting a couple to test out which one works best.

4. Use of Expander Mandrels

Expander mandrels allow you to use bushing dies, standard dies and allow you to set the neck tension value based on the diameter of the expander mandrel. When it comes to size brass this has worked the best as far as concentricity values are concerned. Since the expander manuals are available in half a thousand increments we should be able to fine-tune the neck tension that works best for us. 

Other things that are going to affect our neck tension value and are going to vary by your process are the neck wall thickness of the cases you’re using. The amount of bearing surface is like caliber. The surface condition of the inside of the neck, something like leaving the residual carbon, can act as a lubricant. Overcleaning your brass might increase the value of your neck tension. The actual length of the neck of the case can affect your value. Whether or not the projectiles have any type of coating whether you’re annealing your brass or it’s been fired multiple times. Even the duration of time between the projectile seeing process and the actual firing can affect this value.