Neck Expansion in Bottle-Neck Cases

Probably not needed for most applications, but if it makes you happy, sure go ahead. Are there even expanders available for specific bullets? All I've ever seen are specific diameters, and usually that is consistent within a given caliber, indeed most cartridges in a given caliber class. (i.e., .308 for most .30 cal.)

For my precision focused loading, I run expanding mandrels. For bulk ammo, I don’t. I use a turret press in my sizing activity, there’s not much time commitment in cranking twice instead of once.

Why would you need an expander for a specific bullet? What would be the design criteria? We’re expanding the inside diameter of an annulus, nothing more, so a fixed diameter mandrel which meets the desired neck tension for a particular bullet is “perfect,” no need to try and complicate things beyond that.

It seems to me that neck expansion is best done in tension, as it has the tendency to self-align. This is especially true if you can arrange to start expansion before the mouth is quite free of the die neck (ie the high expander button in some of RCBS's dies) and thereby benefit from the die's alignment of the brass.

Ideally you'd like to size the neck from outside and not need to expand, but that requires a custom die neck matched to perfect (turned) brass.

The only exception I know of is M-dies, et cetera, because you can't step flare the mouth from inside the case.

edwardware said:

It seems to me that neck expansion is best done in tension, as it has the tendency to self-align.

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I would argue the opposite. A cone isn’t as strong when pulling out of it as it is when pushing inward. When you run the gear side by side, it’s easy to measure run out, which indicates when PULLING out, one part of the cone yields before the other, and the neck is pulled out of center. Pushing in, alternatively, the conical shoulder is “locked” in place, and less apt to allow asymmetric float as it yields to the mandrel.

JDinFbg said:

why expand the entire neck and over-work the brass when only about one third of the case neck needs to be expanded?

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Bushing die.- Only size the amount needed. No need to size the whole neck.

The unsized neck expands to the chamber after a few firings. It centers the round in the chamber.

suggest you grab the current issue of "handloader magazine". john barsness has an article in there that will answer your question quite well.

luck,

murf

243winxb said:

Bushing die.- Only size the amount needed. No need to size the whole neck.View attachment 849130

The unsized neck expands to the chamber after a few firings. It centers the round in the chamber.

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Bushing dies are great if you have neck turned such you know the ID will be uniform after you size the OD. Fine for a low volume match rifle, not great for a low rigor reloading process for a hunting rifle, or for a high brass volume competition set up.

I use the same Redding bushing die with a .002" larger bushing for unturned brass. Use or dont use the expander.

I have always used the .002" undersized button supplied with the standard die set in the past, but the latest project is a .338LM and I noticed rediculous velocity ES of ~250 fps. that I attributed to insufficient neck tension with the low powder charge that gave the best accuracy, low 6s.

I picked up some expander mandrels in .0005" increments and the .3550 got group size down to low 5s. For this rifle at least I'll add the extra step.

A standard die may size the neck down .010" Then the neck may need expanded .008" to get .002 neck tension.
The idea is not to size the neck to much in the first place.

If i get .0015" neck tension using a bushing/expander or let the bt bullet act as an expander on seating, i cant tell the difference on target at 100 yards.

I would need a more accurate rifle/cartridge.

The dedicated neck expanding die would give more adjustment and should work better. But only with minimal neck sizing first.

Mark me down as being in the same camp as @Varminterror

I use an expanding mandrel on my long range / precision ammo. And bottleneck stuff I load that's a bit more "mass produced" I use the expanding button that is in the sizing die.

I have heard of scenarios on this board where people were having trouble with "sized" brass not fitting....and the root cause ended up being the fact the inside-the-die expander was elongating the case when force was applied to get that expander out of the case. I myself have not experienced that phenomenon.

OR

JDinFbg said:

So, why expand the entire neck and over-work the brass when only about one third of the case neck needs to be expanded?

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In this scenario, the brass is going to be “worked” anyway, once you fire it. Now if you use a bushing sizing die and only size the neck down where the bullet is seated, then yes, it will be worked less.

I am a hunter so I use a full length sizing die for all of my rifle cases, then I trim the case necks, then I anneal the case necks as needed, and then I use a case neck expander die plug to increase the diameter of a short portion of the case neck to control the tension on the bullet. The expander plug is the same diameter as the bullet. One turn on the stem of the case neck expander die runs the plug down into the case neck about .035. I usually expand the neck about .070. The bullets seat easy with a uniform thumb pressure on the press handle. I don't worry about working the cases as I get good case life for my 25-06, 270 Winchester, 30-06 and 338-06 cases. The system works good for me.

Walkalong said:

If you neck turn, or your brass is very consistent in neck thickness, a bushing die works just fine. Some people like to use the bushing die and the expander in the die, bushing it all down just enough so the expander does minimal work. They feel like that (Or using a mandrel in a second step) moves the "inconsistency" to the outside. I feel like if that really works that way, and I have been unable to prove or disprove it with lots of measuring, then the bullet will do the same thing when seated.

All that said, if your brass neck consistency is poor, I would use the bushing/expander or bushing then mandrel.

This is all assuming your rifle/load/bullet can take advantage of such things.

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It's the method I use.

Help me with your logic. Is everyone assuming that the sized cases are to be used only in the rifle that they were originally fired? Is everyone not setting the shoulder back?

The bushing die is all new to me so I am trying to understand the benefits. RCBS has both a full length bushing die for a 30-06 (14834) and a neck sizing bushing die for a 30-06 (14835) and I plan to try one of them. The headspace on a rifle is about .005 and I have tried to set the shoulder back .002 to see if that plan would allow the cartridges to be fired in more than one rifle. Even when fired in the same rifle it didn't work very well for me possibly due to springback of the shoulder or pulling on the shoulder by the expander ball. It looks like I could use the full length bushing die by removing the bushing to size only the body of the case, and then re-set the die above the shell holder and use the bushing to size only a portion of the neck. The un-sized portion of the neck would then center the round in the chamber. I have tried many things in the past, some with no benefit, and this may be one of them for me. Very interesting thread.

243winxb said:

Bushing die.- Only size the amount needed. No need to size the whole neck. The unsized neck expands to the chamber after a few firings. It centers the round in the chamber.

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Never thought about it before but I like the idea of having a portion of the neck unsized. It makes sense to center the round in the chamber. There is an .008 difference in the diameter of the neck in the example used by 243winxv and that has to make a difference in the consistency of the placement of the bullet when the rifle fires.

Bushings may not be a good choice if sizing down more then .008" in 1 step. Sizing necks may require an intermediate sizing.
I have 3 bushings .270" 269" and .268" The first 2 will produce an OD same as the markings on the bushings.
The 268 bushing will produce an OD neck around .2678" using neck turned brass. A little smaller then what is marked on the bushing.

This is a fun experience for me. A fired case in my favorite 30-06 measures .339 in neck diameter. A sized case with the expander ball pulled through the neck measures .333 which is a difference of .006. A case with the bullet seated measures .335 which expanded the neck by .002 which follows the example by 243wubxb. Now, if I size only half of the neck I can keep the case neck lined up with the barrel and perhaps improve my group size. I need a bushing die that gets me close to the .333 OD neck diameter without using the expander ball. Sad to say but there's a .004 slop in the bullet fit in the neck which is almost a big as the headspace. Thanks for the logic in this thread.

sage5907 said:

Help me with your logic. Is everyone assuming that the sized cases are to be used only in the rifle that they were originally fired? Is everyone not setting the shoulder back?

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I use FL Bushing dies and just bump the shoulders back a couple .001s.