NEW Expanding Mandrel Die from L.E. Wilson

I do a lot of shooting with loads using brand new brass. And the results can be downright impressive! One challenge I’ve had with loading new brass (a frequent issue) is excessive neck tension. New brass necks tend to come a tad undersize (0.001″-ish). There are also situations where you’ll find dented or imperfect case necks (not perfectly circular opening). An expanding mandrel die can help with these issues, and that’s the subject of this article and video: the new Expanding Mandrel Die from Wilson Tools and Gauges (L.E. Wilson). Let’s check it out!

What is an Expanding Mandrel Die?

Above: Expanding 6 Dasher Brass using the Wilson Expanding Mandrel Die and the Forster Co-Ax press

At the heart of an expanding mandrel die is a profiled rod (the mandrel itself) which is pushed through the neck of a shellcasing in order to expand the neck to a particular diameter. The mandrel is not a cylindrical rod, there is a larger diameter section towards the tip that does the expanding.

The resultant case neck diameter (after expanding) depends on case neck diameter, thickness, and hardness. This is because of “spring back”- the brass does not fully expand to the diameter of the sizing section of the mandrel, it “springs back” just a bit. It’s therefore a good idea to measure the inside neck diameter before and after neck expanding.

Here are some numbers from my testing with new 6 Dasher Brass from Alpha Munitions:

  • Expander mandrel diameter: 0.243″
  • Initial inside neck diameter (new brass): 0.240″
  • Final inside neck diemeter (expanded brass): 0.2415″
  • Bullet diameter: (6mm) 0.243″
  • Final interference fit, bullet to neck: 0.0015″

From our analysis above, you can see how our interference fit was cut in half: from 0.003″ (new brass), down to 0.0015″ (new brass with expanded neck). This is perfect! And we don’t have to worry about dented or crushed/deformed necks either.

Expanding Mandrel Die: A Flexible System

The Wilson Expanding Mandrel Die is available complete with the mandrel of your choice, and you can also order mandrels separately (which are swappable in seconds) for other calibers to add to the flexibility of  your setup.

Great Results with 6 Dasher

One of the most important factors to consistent velocity is consistent neck tension. And that’s where this expanding mandrel die comes in very handy.

The numbers don’t lie, and with this expanding mandrel die I saw some phenomenal results with my first loads using new Alpha Munitions 6 Dasher brass! The picture above shows 5 shots mid-way through my initial load development for 6 Dasher (more info coming in future stories) and I was amazed by that!

And things got even better, here’s the best new-brass chronograph data I saw during this load development exercise:

With a standard deviation of 2.2 FPS, and an extreme spread of 6 FPS, it just doesn’t get much better than that! What’s more: these new brass loads produced some STELLAR accuracy as well, more on that in my next story (6 Dasher load development). Let’s just say these loads have produced benchrest-level accuracy. I couldn’t be more happy! One thing is for sure, I’ll be using these expanding mandrels a LOT more in the coming years.

Get It Here

If you are interested in the new Expanding Mandrel Die from L.E. Wilson, check out the following product pages:



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