The Science of Neck Tension

[mdesign]

We've all read the post...."I changed my neck tension and my groups got better/worse".

My question is why? Why does neck tension effect accuracy?

Think about what the neck of a case does, it holds the bullet in position in relationship to the case and the bore. Weither it squeezes it hard or soft the position is the same. What changes with neck tension is the ease in which the bullet is released.

The less pressure that it takes to release the bullet from the grip of the case, the less the impact to the bullet when it engages the bore so it is deformed less and travels straighter down the bore????

Anyone have a better understanding of this subject they could share with us?

 

[Victor N TN]

Re: The Science of Neck Tension

Not exactly on topic. But it has a bearing on the original subject.

Have you ever noticed that most of the really accurate cartridges have a similar outer shape? Look at a standard 223 round. Then compare it to a 22 PPC round. The main difference is the shape of the case. They both can have a 50 to 55 grain bullet. They both use basically the same burn rate powder.

There have been a few articles written in the past years that the shape and ignition of the powder column have a lot to do with the inherent accuracy of the round. One of the authors suggested that having the right neck tension holding the bullet at a given tension helps the powder get started burning in the optimum manner.

While doing tests for benchrest rifles I have had neck tension very tight to barely holding the bullet in place. I don’t have my notebooks in front of me. But I do remember it was neither of the extremes. The .002” stated here on the hide in several places is a good place to start. But if I wanted to change it, I would do so in .0005” (five ten thousandths, or half a thousandth) increments. While most makers don’t show bushings in half thousandth steps. If you call they can usually come up with something for you. I have seen bushing in .0005” steps before. But I can’t remember who it is that makes them or the material they’re made from. But they are out there.

I hope this at least helps get things going on the discussion.