Expanding the range of your expander

[Spindrift]

As we all know, brass is a springy affair. In fact, there are several circumstances where we rely upon this very springiness (should be a word. Maybe it is). For instance, when we empty the chamber of our just- fired brass.

Like probably many of you, I use expander dies to prepare my just- sized necks for my cast bullets. Sometimes, for whatever reason, I’ve made a cartridge where the neck was expanded twice (typically, because I had to adjust the flare). This cartridge will usually hit outside the group, due to the neck tension being different to the other cartridges.

Why will passing the same expander through the neck a second time change neck tension of the finalized cartridge?
With the first pass, the brass will spring back to an internal diameter slightly smaller than the expander. The next time, it will spring back less.
I realized this effect could be utilized if less neck tension was called for, but I didn’t have the right expander to do so. I made some measurements to quantify the effect of a second pass with the same expander plug.

Using .30-06 and .35 Whelen brass, I found that the second pass with the expander further increased the outside diameter just shy of a half thou, 0,00047.
Enough to be relevant? I believe there can be instances where it is!

 

[Ian]

Absolutely relevant. Just don't mention it on the CBA forum or you will get drug through the mud and clearly told that your assertions are incorrect.

 

[Snakeoil]

Absolutely relevant. Just don't mention it on the CBA forum or you will get drug through the mud and clearly told that your assertions are incorrect.

Well, it's hard to argue with empirical data. If it measured bigger after the second pass, it was not due to divine intervention.

 

[Ian]

Well, it's hard to argue with empirical data. If it measured bigger after the second pass, it was not due to divine intervention.

They won't believe you unless you gather enough empirical data to exceed the amount that the last guy produced to prove the opposite. It's a war of statistics and I am too tired to argue with myopic people.

Neck tension variances are often a very large contributor to flyers and erratic groups in my experience. If, or how much it matters in a particular rifle/ammunition system is easily tested by attaching a pull-scale to the reloading press handle and recording the maximum reading, then sorting into like groups and firing them in order and overlaying the targets...or mixing known tensions and firing them in order on one target while recording the placement of each shot.

 

[fiver]

but that's assuming the easy ones didn't simply go in the case straighter.
or had less flair on the top of the gas check.
more measuring.... LOL

it's like the Baron Harkonen thought and the Emperor said out loud.
plans within plans within plans.

anyway you don't have to do better work, you just gotta write your words more convincingly.
i'm good with hey i measured this and this is what i found.
that gives me enough information to get out my own tools and see what i get.

 

[Ian]

I gave up on convincing people of anything and have been much happier for it. I show what I did, explain the details, and anyone is free to verify my results for themselves. A few have actually done it.