Reloading Bench — How to Optimize Case Neck Tension
by Sierra Bullets Ballistic Technician Paul Box
One thing that plays a major role in building an accuracy load is neck tension [one of the factors that controls the “grip” on a bullet]. I think a lot of reloaders pretty much take this for granted and don’t give that enough thought.
So, how much neck tension is enough?
Through the years and shooting both a wide variety of calibers and burn rates of powder, I’ve had the best accuracy overall with .002″ of neck tension. Naturally you will run into a rifle now and then that will do its best with something different like .001″ or even .003″, but .002″ has worked very well for me. So how do we control the neck tension? Let’s take a look at that.
First of all, if you’re running a standard sizing die with an expander ball, just pull your decapping rod assembly out of your die and measure the expander ball. What I prefer [for starters] is to have an expander ball that is .003″ smaller than bullet diameter. So for example in a .224 caliber, run an expander ball of .221″. If you want to take the expander ball down in diameter, just chuck up your decapping rod assembly in a drill and turn it down with some emery cloth. When you have the diameter you need, polish it with three ought or four ought steel wool. This will give it a mirror finish and less drag coming through your case neck after sizing.
Tips for Dies With Interchangeable Neck Bushings
If you’re using a bushing die, I measure across the neck of eight or ten loaded rounds, then take an average on these and go .003″ under that measurement. There are other methods to determine bushing size, but this system has worked well for me.
Proper Annealing Can Deliver More Uniform Neck Tension
Another thing I want to mention is annealing. When brass is the correct softness, it will take a “set” coming out of the sizing die far better than brass that has become too hard. When brass has been work hardened to a point, it will be more springy when it comes out of a sizing die and neck tension will vary. Have you ever noticed how some bullets seated harder than others? That is why.
Paying closer attention to neck tension will give you both better accuracy and more consistent groups.
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Tags: Annealing, Bullet Release Force, Neck Bushing, Neck Tension, Reloading, Sierra Bullets
When are they finally going to combine the expander ball with a bushing die?
If you don’t neck turn there is no way to control the inside diameter of the neck by using a bushing on the outside.
Expander balls should be available is different sizes in at lease 0.0005″ increments.
What you want is available. Whidden makes expanders in small increments and several die makers make bushing dies that can be used with expanders. The Whidden expand/decap parts also fit Redding dies.
With all due respect, the spring back after the expander passes through the neck is inward, toward a smaller diameter, so if you use an expander that is .003 under diameter, the resultant neck tension will be greater than that, not less. If you do not believe me, run the expander back through the neck and feel the resistance.
When you first take up reloading and read the basics at the front of the manuals it seems straight forward enough. Then you start to realize some of the more advanced and finer details for reloading practices are not so black and white.
To achieve the best results you realize you need to expand your reloading knowledge, buy more reloading equipment, spend time working up loads, measure/record everything, and maybe even buy a custom rifle. So much for cut and dried. Lol. But it is therapeutic and addicting.