Do I need a dedicated expanding mandrel?

[Bigdad123]

I'm having trouble understanding the difference in a expanding mandrel die like Wilson and the expander that comes with my Hornady Match bushing sizing die. They seem to do the same thing. What is the advantage of the Wilson mandrel over the Hornady die with expander button?

 

[LVLAaron]

The mandrel should be much more consistent. Switching to an expanding mandrel on my 223 loads was the single largest improvement to my group sizes.

Mandrels also come in many different sizes so you can control neck tension

 

[butchlambert]

My expanding mandrel works with the mandrel of my neck turning tool. I control neck tension with my carbide neck bushings.

 

[dkhunt14]

I'm having trouble understanding the difference in a expanding mandrel die like Wilson and the expander that comes with my Hornady Match bushing sizing die. They seem to do the same thing. What is the advantage of the Wilson mandrel over the Hornady die with expander button?

When you pull an expander button out of a case, it can change the dimensions by stretching the brass. It is alot smoother to run a mandrel in and I never saw it change the dimensions of a sized case except the diameter of the neck. Matt

 

[Bigdad123]

Thanks for the quick replies. So difference is the mandrel expands the neck on the upstroke instead of the down stroke and that improves runout and prevents case stretching?

 

[butchlambert]

A mandrel on the way down and the button on the way up.

 

[PigButtons]

Sequence of events for expander ball in common die:
1) case mouth moves past the expander ball fairly untouched
2) neck and body are squeezed down to size allowing for spring back
3) as the case is extracted the mouth is forced open by the expander ball being pulled through it

 

[jepp2]

What is the advantage of the Wilson mandrel over the Hornady die with expander button?

An expanding mandrel avoids the problems caused by the expander button on your sizing die.

I spent over 2 years trying to improve the TIR of my loaded rounds as measured on the bullet. I learned a lot and spent lots of $$.

Most current production full length sizing dies seriously undersize the case neck. This is intentional, so no matter the case neck thickness, it will be sized down enough for sufficient case neck tension. The expander opens the case neck back up, so your neck tension is within an acceptable range.

What I found was even though I was using a carbide expander, lubing the inside of the case neck, and setting my expander high enough so it passed through the case neck as soon as the neck left the neck portion of the sizing die:

"If the expander button has to expand the case neck more than 0.002" it will significantly affect the case neck TIR in a negative fashion."

Maybe you don't know how much your sizing die is undersizing the case neck. Easy enough to find out. Size a case with the expander removed and measure the neck OD. Then size a case with the expander in place and size that case. Measure the neck OD.

 

[D-4297]

The key to using a expander mandrel , after the case has been bushing sized , is to NOT over-work the neck by using a bushing that reduces the diameter of the the neck to a , "to small a diameter" . In sizing my .308 round , I use a bushing that will reduce the neck diameter to to .3065 - .307 , and my mandrel expands the neck back to .3075 . Over-working the neck brass causes the greatest inconsistencies in seating pressures , variance in SD / ES , and results on the target . IMO .