Expander Balls

[Twud]

I have never understood the purpose of an expander ball. Once the round is fired the expanding gasses open up the neck diameter. The diameter now needs to be reduced to hold the next bullet and clear the chamber, but the expander ball would only seem to open it up. What happens inside the die to the neck? Wouldn't make sense to size it down only to have it go back through the expander ball on the down stroke and be opened up again.
Why do bushing die not have one?
Help!
Mark

 

[rayjay]

Most brass doesn't have necks with a consistent thickness. If you only size the OD then the ID is not round. The expander ball makes it round on the ID. Mass market 'SAAMI spec' dies size the neck more than is needed and the ball brings it into spec.

 

[Cheechako]

Mark

Not all brass is created equal - some have more/less neck wall thickness than others, even cases of the same lot.

If you size the neck with a bushing die, the cases with the thicker necks will have more bullet tension than those with the thinner walls. That's why you either turn the necks to a uniform thickness or use a bushing of the size appropriate to your brass.

A standard die has a fixed diameter neck sizing portion so you have to approach the problem differently. You size the neck down smaller than is actually needed and then pull the sized case over the expander ball which sizes the inside of the neck to the same dimension on all cases regardless of neck wall thickness.

Another approach to the expander ball is to size the neck down in a sizing die and then run the necks over and expander mandrel of the correct size. This makes for a little more uniform case neck since you are pushing the neck over a die rather than pulling it over one which can sometimes distort the neck.

Sizing and expanding in a regular die works the brass more than a bushing die, which could lead to less loadings before they wear out but the average case will probably wear out from other things,like high pressure pounding) before that happens. For cartridges like granddaddy's 30-30 it probably doesn't make much difference either way.


Ray

 

[mmcauliffe]

Why do bushing die not have one?
Mark

My Redding bushing sizer die came with a expander ball in it...I took it out, but it came with one.

 

[memilanuk]

You can look at it one of two ways.

One, you can think of it like a Wilson neck die designed to be used in an arbor press,or with a mallet). These are nominally intended for minimum chambers where the brass doesn't expand a whole lot to begin with. A slight squeeze of the neck is all thats required to make the case neck grip the bullet again. A threaded 7/8x14 bushing die like a Redding Type 'S' does more or less the same thing, but can also do F/L sizing in the same step if you purchase that kind of die.

Two, you can look at it like a regular full length sizing die,which it is). It's designed to size the whole neck, not just part. The catch is that a regular F/L die squeezes the neck down *too far*, and then the expander ball opens it back up. Because it has to work against a neck thats been squeezed too much... the expander ball tends to pull on the neck,typically unsupported at this stage in the evolution), causing stretching, concentricity problems, etc. With a bushing F/L die, you can size the bushing to squeeze the neck just a hair bigger on the ID than the expander balls OD, so it just kisses the inside of the neck on the way thru. This way you don't overwork the neck, you can make sure that any miscellaneous dings get worked out of the case mouths, and the necks get opened to a consistent diameter from the inside set by the expander ball, rather than the neck bushing which works from the outside. This works especially well if you use a floating carbide expander ball,available separately from Redding) which is harder, slicker, and has a smaller surface contact area and floats to ensure the ball is centered in the case neck.

Either way works, but I tend to view things from the latter perspective.

Monte

 

[Clark]

I paid $100 for a Sinclair concentricity gauge, and in the box was a little piece of paper like from a fortune cookie that said, "You will probably find that the problem is the expander ball."

I now know that the problem is using the expander ball AND the sizer in the same step. The expander ball goes in easy, but while it is in, the sizer makes the neck smaller. To get out the expander ball must pull through the neck. It the cartridge is being held by a conventional case holder that is asymmetrical, the neck is going to get bent. Not enough to see, but it can be measured. Probably another .004" of runout.

If one takes the expander ball out, sizes the brass, puts the expander ball back in, and expands the neck while pushing, only about .001" of run out is caused in that step.

Curiously, almost nothing can be done about crooked necks, but fire forming to a concentric chamber.

I have 6,000 rounds of .223 brass that my .245" bushing in my Redding S die gave .001" of additional runout. The only practical thing I can do is shoot it to fix it.

If I open the neck way big with a mandrel or expander ball, the sizing die will not straighten it, becuase before the die gets contact with the body, it has already been following and sizing the crooked neck.

What does it all mean?
Don't use the expander ball.
Use a decapping die to get the spent primer out.
1) In benchrest, the chamber neck is so tight, the brass does not reach the elastic limit, and so the neck is not resized.
2) In varmint class accuracy, if the chamber neck is as small as possible without necessitating neck turning, then it can be sized with an S die and bushing or with a Forster factory honed out die. If the chamber is SAAMI sized, use the Forster factory honed.
3) In deer hunting accuracy, use the Lee really good buy $10 dies with the expander ball in place.