If the problem with bottleneck cases growing is due to forces applied inside of the neck by the expander ball, why not remove the expander ball, and then use a second die to bell the case mouth, as is done with straight wall handgun cartridges?  Would this leave you with excessive neck tension?  And if that's the case, would the use of boat tail bullets, with their easier alignment for seating, alleviate that problem?

The sizing die sizes the neck to small without the expander ball and belling the case mouth wouldn't be a very precise way to obtain the correct neck tension.

You could get a Redding Type "S" bushing die and use the correct bushing to get the neck ID you want for proper neck tension and not use an expander ball, I use these dies with a carbide expander and don't notice any growth at all.

That is not the normal mechanism for case growth.

The case is always slightly shorter than the chamber to allow reliable chambering.

The firing pin drives the case forward as far as it can.

The front of the case then sticks to the chamber walls as pressure grows.

The pressure finally gets high enough to force the head of the case against the breech, stretching the case slightly.

I use a FL sizing die without an expander ball or mandrel that uses collets to size the neck OD of the brass.  Like EWP I see no brass gowth that requires length sizing.  You do need a set of mandrels to match the mandrel size to the different brass thicknesses to obtain the desired neck ID and the resulting neck tension.  This method prevents the double sizing of the brass neck.

Normal sizing is done by first lowering the expander through the neck followed by the neck sizing portion of the die to make the neck have a smaller ID than the expander.  Then the expander is pulled through the neck to expand it to the desired neck ID.  This is the double working of the neck each sizing operation.

The case will grow regardless of whether you use an expander ball or not. The firing sequence swell the case until it is form fitted to your rifle's chamber. As soon as you run it through a die you squish the case back close to normal dimensions. The expanded brass, now being constricted. has to go somewhere. That's why they get longer.

You can reduce expander ball induced growth with Redding's "S" dies. You can also buy Forster's dies and they will custom hone the neck dimensions to whatever you specify. I have Forster .223 dies in .2450" and .2445" custome neck dimensions. Either will work great and only require .001" to .002" expansion from your ball or mandrel. Reducing stress on the brass is a good thing.

Redding (and probably others) also offer carbide expander balls that slide right through the necks with the greatest of ease. Another option worth considering.

If that's true, then why do my 9mm or 45 cases not grow, even when loaded hot?

Bummer.  I find that RCBS X-Dies actually do work to eliminate case growth, but they don't make X-Dies for 7.5x55 Swiss

Sometimes there is a difference between theory and practice.  I use an FL collet type die and my brass does not grow in length, even over multiple reloads.  My poor trimmer sits in my bench, unloved.

They are straight walled pistol cases, they have no shoulder to push out.

I know the precision reloaders worry 'excess' neck tension but I have a question.  





Doesn't high accuracy rely on consistent neck tension rather than a specific amount?  For example, I trim my precision .223 brass with my Dillon trimmer and die and don't re-expand the case neck after trimming so my necks are tight, but consistent.  





I settled on this because I didn't see any difference in accuracy at 300yds using my 68grn Hornadys (my rifle likes them better than 69grn Speers) between some test cases with the neck expanded using a carbide expander ball vs those I just left as they came out of the tighter Dillon trim die.





My measurements show me that both methods give consistent neck sizes and I didn't see any tightening of my groups with the expanded case necks.  However, to be fair, I'm a 1MOA shooter at 300yds (< 3.0") so there are likely lots of shooters who can hold tighter groups and maybe that's where it comes into play.

 

And, pistol chamber pressures are about a third of centerfire rifles.

 What is a Full Length Collet type die and who makes it?  The only "Collet" sizing die that I am aware of is the Lee Collet Neck Sizing Die.

I also have the Lee collet neck die and it does not size the body or bump the shoulder back, pretty worthless for use with an AR unless used with a body die.

I do not use Lee dies.  The die I have is the Redding Type S Bushing Style Full Sizing Die, part number 77111.
For reference:  Redding Competition Dies

Better Link:  Type S Bushing Dies

 AH, a bushing die, not a collet die, didn't think there was any FL Collet dies out there, but ya never know.

Sorry for the terminology confusion Steve.

That's the same dies I use, the Nitride bushings and carbide expander ball make sizing effortless and give you much more control over the neck sizing.

This is essentially a body die.  Body dies are used by bolt rifle guys who usually neck size only.  After time the repeated case stretching from firing work hardens the case somewhat so it does not spring back as far and closing the bolt becomes more difficult.  Rather than dealing with a FL die, they use a body die only when needed to bump the shoulder back 0.002" or so to ease chambering.  The difference between a bod die and an FL die with the expander removed is that the body die is opened up in the neck area so it isn't touched at all, leaving that sizing for the neck die to handle.