As above chaps, why design the die to construct the neck down too far and then expand it up again?

What is the theory behind it?

I think the idea is that the die makes every case with the same inside diameter- regardless of the difference in neck thickness.

Saeed is most likely correct. With the various brass manufacturers inability to produce brass that held to strict minimum dimensions, the dies have to "oversize" the necks and then pull the expander ball back through to open them back up.

Of course the great variance in chamber dimensions adds to the problem as well.

The expander ball would also straighten out any inward dents in the neck area!

It is also used to NECK UP brass to a larger caliber ex. .270 to .30-06.

Hip

Right; it's to compensate for all the tolerances in brass, chambers, and dies. note that the hand operated bench rest dies don't use inside neck expanders; but instead rely on perfectly trued necks. You could have custom dies made, or use the bushing type, to do the same thing.
Also note that the small "ball" is no longer in vogue, but the longer tapered types are.
I personally think that dies size necks way more than required or desired, but they want to make sure that they work with all brass thicknesses.

Well, constrict brass and there will be some spring back. The expander ball equalizes that, so, between constricting and expanding you have consistency. That is my theory.

quote:

Originally posted by Saeed:
I think the idea is that the die makes every case with the same inside diameter- regardless of the difference in neck thickness.

After this post was made no other post was needed

The issue that the expander ball is incorporated into the sizing die to combine three operations into one stroke of the press handle - decap, full length size, and to uniform the neck. Some presses also incorporate a re-prime in the operation.

This works fine until one desires to extend the life of brass by reducing cold work or wants to adjust the neck tension. At this point the expander ball wants to disappear from the sizing stroke and be run in a separate operation.

Redding recommends with their bushing dies if you have .002 or more neck thickness variations to use the expander that comes with there dies.

If you did not turn your necks the expander pushes the irregularities to the outside of the case neck. And I have seen case necks with over .009 thickness variations.

Forster will hone their dies neck to your desired diameter. And they recommend the diameter be .004 smaller than the neck of a loaded round, and use the expander.

Are Your Sizing Dies Overworking Your Rifle Brass?
http://www.massreloading.com/d...erworking_brass.html

quote:

Originally posted by ted thorn:

quote:

Originally posted by Saeed:
I think the idea is that the die makes every case with the same inside diameter- regardless of the difference in neck thickness.

After this post was made no other post was needed

Unless you turn your necks to uniform thickness, tell me why simply seating a bullet won't accomplish the exact same thing. If you have a case that's say .002 thicker on one half of the neck than the other half and you FL size it and then expand it you will still have a case that is .002 thicker on one side of the neck, but just slightly smaller in diameter. Once the bullet is seated, one half of the case neck will still be .002 thicker than the other half. If you take an identical case and FL size it sans expander and then seat a bullet, you will have a loaded round identical to the first one.

I see no reason to use an expander unless one is necking up. Also if you ever have a stuck case it will be WAY easier to get it out of the die without that pesky expander in the way.

If you use bench rest dies custom make for your chamber and brass, then sure, you do not need to inside neck expand.
But the standard die makers have to compensate for chambers made for 100 years and brass made by many different makers; so they generously size the brass, smaller, and then bring it back up to size using an inside neck expander. That is one size, fits all theory. If you try to seat a bullet into a neck without doing that, you will crush a lot of brass, especially with flat base bullets.
That is why.

quote:

Originally posted by dpcd:
If you use bench rest dies custom make for your chamber and brass, then sure, you do not need to inside neck expand.
But the standard die makers have to compensate for chambers made for 100 years and brass made by many different makers; so they generously size the brass, smaller, and then bring it back up to size using an inside neck expander. That is one size, fits all theory. If you try to seat a bullet into a neck without doing that, you will crush a lot of brass, especially with flat base bullets.
That is why.

I've never crushed a case doing it my way. Even flat base bullets have enough roundness at the base so that they seat easily. See uploaded pic. I've run a .25-06 case into a stemless .25-06 die and seated a 6.5 bullet into that case with no crushing of the neck or other problems. It does give a bit of hourglass appearance to the loaded round. As far as I can tell the only thing that the neck needs to be is just smaller in diameter than the bullet your going to seat into it. If it's really out of whack as far as wall thickness goes then the neck should be turned or the cases scrapped.
In the picture the top case had a .264 120 grain Sierra spitzer seated while the bottom case had a .264 Sierra 140 grain BT match seated, both in .25-06 cases sized with no expander.

You won't get away with that with all calibers and dies.

quote:

Originally posted by dpcd:
You won't get away with that with all calibers and dies.

Right now it works for .243 win, .25-06, .25/.284, 6.5-06, 6.5-06 AI and .280 Remington

OF course I don't resize my 6.5-06 cases with a .25-06 die, but I could if I wanted to.

dpcd is correct,this will not work for all calibers,you will get some damaged cases.

quote:

Originally posted by Bill73:
dpcd is correct,this will not work for all calibers,you will get some damaged cases.

True, but when it works it saves you the hassle of lubing necks and cleaning them afterwards. When I did lube I used a scosch of sizing wax and a Q-tip.

To bad someone from Redding, RCBS or other die manufacturer doesn't chime in on topics like this.

quote:

Originally posted by dpcd:
If you use bench rest dies custom make for your chamber and brass, then sure, you do not need to inside neck expand.
But the standard die makers have to compensate for chambers made for 100 years and brass made by many different makers; so they generously size the brass, smaller, and then bring it back up to size using an inside neck expander. That is one size, fits all theory. If you try to seat a bullet into a neck without doing that, you will crush a lot of brass, especially with flat base bullets.
That is why.

Like this?

I had a few new .280 Remington cases that I had set aside years ago as having crooked necks. Today I was looking for a case to use to make a seater dummy for my 6.5-06AI so I ran one of the .280 cases into my 6.5-06AI sizing die. The first couple collapsed the shoulder per the pic. The next few worked fine. Normally I wouldn't recommend making a large change in diameter in one step.

I've had my share of crumpled cases over the years. We hope to learn from our mistakes. Or as Otto Von Bismarck said,"I don't want to learn from my mistakes.I prefer to learn from the mistakes of others."

quote:

...

It is also used to NECK UP brass to a larger caliber ex. .270 to .30-06.

...

Most of my dies are 30 or more years old, so the expanders are "buttons" that are too short to reliably neck up cases without damaging them.

For cases up to .30 caliber I made long taper expander plugs for my Lyman M2 expander die that will neck up cases without damaging them.

When I got my .375 RUM I made a pointed long taper expander plug that replaces the de-primer rod of a RCBS .375 FL Z die. With a little Imperial Size wax in the mouth of a case, I can easily and with one stroke, expand the necks of 7mm and .300 Rum cases to .375. I've necked up over 100 of these cases without a single failure.

Keep in mind that you can buy expander balls in sizes or you can trim a expander ball with a file and some wet or dry paper backed on a file in a drill press if your handy..Done so will not be so tight on a bullet and make reloading a bit easier and save brass wear..Were talking in thousands here, like one, two maybe three at the most..buy or trim...

I took 3 off my 450-400 double rifle expander ball as the brass is so thin, and was being over worked...I then loaded it with a powder that filled the case and the bullet seated real tight even at that, that way I never had to crimp those thin cases and brass lasted much longer..the full case of powder helped keep the bullet in place as did the tighter neck. and I still had the option of a crimp if I needed it, but I didn't. and I didn't crush he shoulder on any more cases.

One reason to use the expander ball might be so you can get the cases on to the case-trimmer's pilot.

As one who used to only reload when I ran out, which could be a matter of years, I would always reread the die's instructions. For some reason, mine didn't bother to mention lubing deep inside the neck, so I just pressed the mouth into the pad.

Over years, I now think this had the effect of wearing down the expander, not a problem until I finally got a proper case trimmer. Then I found resized cases the devil to trim.

My .348 Win cases were very difficult to pull over the expander plug in the sizing die so I bought a die from RCBS that expands the neck on the plunger upstroke of the press. It's meant for cast bullets, but it works for jacketed ones as well.

Trimmimng cases before or after resizing can create a need for a differnet case trim guide, but they come in all sizes..so much depends on the chamber in your rifle..I have a bench rest rifle chamber that all I need to do is add a primber and powder and shoot, don't actually need a resizeing die, well after a number of reloads I might on some cases and not on others, but I do them all now and then..Special dies btw, that basically burnish only. Sometime referred to as zero tolerance dies..

I see no reason to use an expander unless one is necking up. Also if you ever have a stuck case it will be WAY easier to get it out of the die without that pesky expander in the way.[/QUOTE]

Because of the variance in neck tension.

For the best accuracy, neck tension should be consistent from round to round. If brass is properly turned and sized, there's not a real need for the expander button to achieve consistent neck tension.

That is why the use of an expander button is desired for the average reloader.

Zeke