Thin walled 9mm brass, neck tension and Lee Undersized die

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Feb 6, 2013
I have a couple of thousand pieces of mixed headstamp 9mm brass in my reloading inventory. Some of it started as virgin brass, some of it is from factory ammo I personally shot and a bunch of it is range pick-up. I inspect each case for splits or other trouble before I load it. Any piece that gives me pause just gets tossed in the recycle bucket. 9mm is too plentiful to fret over IMO. However, I have quite a bit of Blazer, Speer and FC mixed in that will not give proper neck tension. I have done as much research on the subject as I can and it seems to be an issue for many but not all. I'm pretty far down the road with this and have already done a lot of trouble shooting like: resetting the sizing die making sure it is set all the way down making contact with shell holder, tried belling case mouth less and not at all, measuring expander plug, measuring bullets etc. The problem is isolated to Blazer, Speer and FC brands (of the headstamps I have) hereafter refered to problem brands. If I use Win or RP brass I get a nice coke bottle shape and no set back. I can feel the difference through the press when sizing and seating the bullet. With the problems brands there is almost no resistance when seating the bullet. After seating the bullet, it can easily be pushed into the case 0.015 or more by pressing into the bench. This happens with both X-Treme 124gn plated hp and Precision Delta fmj. There is no change in length measurement of the bullet itself. Many have described these brands of brass as "thin walled" which makes sense and I believe would explain the problem. I have read about the Lee and the EGW undersized die which undersizes by between .001 and .003 depending on which one you get. EGW website says .001 and Lee says .002 to .003. Lee makes them for EGW, but suposedly they are different. The product description for the Lee die says: "Undersized dies work great for bringing back case tension to hold bullets on cases that may be thinner walled."
My question is 1) anybody have this same problem and try the undersize die to solve it? 2) If so, how did it work? 3) Any reason to go with the EGW version over the one directly from Lee or vise versa? 4). Can/should the undersize die be used on all my brass, even those that aren't giving me issues or do I need to keep them separate? Any other advice that I may not have tried is also welcome.
If your using an expander die, you may need to turn it down 0.001"-0.002" to gain the neck tension.

Now if you seating the bullets without expanding your die may be on the outer end of the spec. I have no problem with the brands your having problem with.

I think what your feeling in resistance is just softer brass. It will work harden as you use it.

If it takes over 35# of force to move the bullet it should be fine.
Try the thin brass sized but not expanded to see if neck tension is good. If it is, the expander is too large.

I have 4 different .45 ACP sizers, each one a different ID. I have two different 9MM sizers, both pretty close, but the Lee with its long tapered carbide insert makes better looking reloads.
Those three headstamps are my preferred brass, especially Speer. I've never had a tension problem with them. You don't say anything about crimping. Are you using a taper crimp die?
FC and Blazer are two of my four prefered headstamps. The reason is that, yes, they tend to be on the looser side of things as far as neck tension. They work wonderfully for cast loads. Perfect tension on the larger diameter bullets while not swaging them down in size.

My other two preferred cases, Win and RP, tend to have strong neck tension, often causing the "coke bottle" effect. These get used only with jacketed bullets.

All other brands get tossed.
Those particular H.S.'s haven't been a problem for me. Now I've run into a couple RP's over the years that were too thin, but even so, it's been far and very few between, and with brass that's been loaded a bunch of times.

I would follow check the expander, if the die is so equipped, and also check to make sure your sizing die is within spec..

Make sure your closing the bell up enough with the taper crimp, though you mentioned not belling at all, so I doubt that's the issue.

So how exactly are you determining that neck tension is light? Have you measured set back pounds on a bathroom scale?

FYI, if your bullets are setting back after multiple times feeding them through the firearm, that is a normal effect. We should minimize how often we rack the same round when ever possible to avoid this issue, though I've seldom ever had this problem.

AMERC brass has thinner walls on their pistol cases. I've mic'd them and if I get any range pick ups I scrap them.
Yes, some brass is thinner.
Yes, I had the same problem with mixed brass.
I got the "U" from EGW. No more problems. I use it on everything now.
Changing the expander doesn't have anything to do with it.
Most people condemn the RP as "thin walled." Haven't heard of Speer or FC blamed for being thin walled before.

Best bet, rather than messing around with different expanders, etc., is just toss the Lee dies and get a good RCBS set. Seriously.
Yes, some brass is thinner.
Yes, I had the same problem with mixed brass.
I got the "U" from EGW. No more problems. I use it on everything now.
Changing the expander doesn't have anything to do with it.
Not always true. Sometimes the expander is to blame. That is why it needs to be tested with it out of the mix to make sure the sizer is sizing the brass enough first.

And of course, sometimes it is the sizer. I have had that happen a couple of times. I bought an EGW Lee U die for one, and bought an RCBS set that cured the other.
I have tried it with no belling at all, but the problem brass still has noticeably less neck tension than the Win or RP. I have not measured the lb force required to cause the setback. I will make a couple of dummy rounds and cycle them through the pistol and take measurements. I was just reacting to the rounds made with those headstamps failing the bench press test. I don't like to see the bullet move at all when I press it into the bench with moderate force. Seems like if it were a problem with my sizing die, I would have the issue with all brass, not just certain headstamps.
I made up two dummy rounds, one with Blazer and the other WIN. Each with no belling on the case mouth. The Blazer, as is typical seated .002 deeper to begin with compared to the WIN. I cycled each through my XD9 sub compact from the magazine three times using the slide release. Blazer set back: first cycle 0.005, second cycle 0.004 and third cycle 0.004 for a total of 0.013 set back. WIN set back: first cycle 0.002, second cycle 0.001 and third cycle 0.001 for a total of 0.004 set back. I know, I know, don't cycle the same round multiple times and you have no problem. That's not really my point.
Sounds like the sizer is too big. Two options. Buy a U die, or try another sizer. It can be frustrating when a sizer is too large.

As I posted, I have four .45 sizers and all are different. My first .45 ACP sizer (RCBS) was too big, it worked on all the head stamps I had besides RP. I called RCBS and they sent me another sizer, but it was super tight, so I ended up buying a Redding. It was perfect, but the carbide ring came out. (Had it happen on another brand in .38 Spl as well.) I glued it back in but it eventually came out again. I got Redding to replace it but the replacement had a poorly radiused entrance and made a ridge on the brass. I called them and they told me I was sizing it wrong. I bought a Lyman sizer and it is about perfect.

Let us know what you decide and how it works.
I had the same problem several years ago with R-P brass in 45 ACP.

The Lee Undersize resizing die solved the problem.

No other head stamps had this problem, and I used the Lee "U" die only with this head stamp. I tried it with others, but gave up on that practice quickly.
Again, seriously, save yourself a lot of grief and get a new set of quality dies. Seeing movement when you do the press test means you have a problem sizing die if you haven't even belled at all.
Sounds like the sizer is too big. Two options. Buy a U die, or try another sizer. It can be frustrating when a sizer is too large.
13 posts, and finally there's the answer.

If the expander was the problem, it would be affecting all your cases, lol.

Buy a new sizing die.

And if you use a SS press, stop sorting by headstamp. That's useless. Some FC and Win cases are thin, too. And occasionally, some of your R-P/Speer/Blazer will be fine. Just pay attention to the feel when you expand, and you'll know which cases won't give you good neck tension. Pfft... pfft...pfft...whoosh!
Thanks for all the replys guys. I will let you know what I decide and how it turns out.
I started using a Lee U die when I bought a Springfield RO and it would not run 100% using a Dillon sizer. Now use it exclusively. I get the Coke bottle look on most loads but they work! I notice that some brands of brass size much easier than others, Blazer is the first to come to mind. I attribute that to being softer, not thinner.
I had exactly the same problem with 9mm when I used Hornady dies. The only brass I could use was Winchester. All others suffered from bullet setback. The worst was when I tried Speer and Federal brass - I could push the bullet into the case with one finger.

I sent the dies back to Hornady with samples of resized brass, and they sent the dies back to me with a note saying they're within specs, no reason for setback was offered.

I bought a U-die and no more setback with any brass. I have since switched to a Dillon 9mm sizing die, which does not size down the brass as much as U-die, and I have great results with all headstamps of 9mm brass.

I still use the Hornady expander die, so I concluded the problem was that Hornady sizing die was not doing the job.
Gadawg88, what is the OD of your 9mm cases AFTER going through the sizing die? Nobody bothered to ask, MIGHT tell us something.
Brass varies from brand to brand and lot to lot in no predictable way.

The last thin 9mm I found was Winchester. My "powder funnel" is OK, so I bought a EGW U die. After I worked my way through that phase I went back to the standard Dillon sizer.

I use the U die for loading 115 gr JHP for defense weapon practice.
The standard die is fine for 125 gr coated and 147 gr plated I have been loading for IDPA.

I also have a .45 U die and a case cannelure tool for loading 185-200 gr JHPs. Even though they are only practice loads, I still do not want them setting back in a carry gun and hurting my confidence in the weapon.
JamieC - Gadawg88, what is the OD of your 9mm cases AFTER going through the sizing die? Nobody bothered to ask, MIGHT tell us something.
After sizing (no flare) averages of several pieces
Blazer OD = .374, ID = .354, brass thickness = .010 * 2 = .020

WIN OD = .372, ID = .350, brass thickness = .011 * 2 = .022

I don't have a micrometer, so these are coming from my calipers. The actual difference in brass thickness may be slightly less than the .002 indicated above. The .004 difference in ID is where the neck tension is being lost. Is this due to a difference in brass hardness/softness and spring back after sizing? Can anybody tie the bow around this package? I have a U die on its way to me already.
I bought a set of dies that had the wrong neck expander in it. Called the factory and they sent me the correct size.
I'm mostly reload 9mm, between 200-500 rounds per week, using a Lee Classic Turret. The only cases that give me a problem are TulAmmo. These are brass cases that come in cylindrical plastic boxes. The cases seem to be quicker than any other case. I can always tell when one of these cases in the press because it feels different. I discard every one that I encounter. I have not measured it but I suspect that the case is so thick its swages down the bullet to smaller than what it should be.
Dude, the sizing die sizes the O.D. to a uniform diameter. It needs to size the brass to a smaller I.D. than the expander is. The expander sizes the I.D. to a uniform size. This is where your neck tension comes from. Your problem with the thin brass, is the sizer is not making the I.D. small enough to be engaged by the expander. This is why the U die solves the problem. It will size all of the cases I.D.s smaller than your expander.
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