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

[JamieC]

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'm missing something, ASSuming a bullet OD of .356", the Blazer brass is .002" smaller than the bullet. My understanding is the bullet needs to be at least .001" smaller than the brass for good tension. Heck, the Winchester is .006" smaller but you're not having problems with those. I went out and pulled several loaded bullets out of one of my boxes, tried pushing 'em into the bench, nothing moved, didn't pay attention to head stamps though, now that I think of it, the only ones I checked were the Bayou Bullets, I didn't check any of my Precision Delta. I'll have to give them a push, see if there is anything to be concerned with. I've loaded quite a few 9mm, haven't had any issues although I haven't checked for set back problems, no reason to....till this thread, LOL.

 

[Gadawg88]

I'm using plated and FMJ with a dia. of .355. If I was loading lead at .356, the Blazer would probably be ok.

My understanding is the bullet needs to be at least .001" smaller than the brass for good tension.

. Think you meant bigger, not smaller. In my experience, you need at least .002 to .003 for acceptable neck tension.

I didn't check any of my Precision Delta. I'll have to give them a push, see if there is anything to be concerned with.

The 9mm is a high pressure round to begin with, so setback can lead to over pressure, particularly if you are at the upper end of the load range. Not trying to cause any unnecessary worry here, but it is something to test for and be aware of. Even with the Blazer brass I am having the "problem" with, I could probably load it and shoot it with no problems, assuming it only gets cycled once. But when it comes to reloading, I don't like relying on "probably" and assumptions.

 

[Potatohead]

No trouble with those brands. Just a thought, I had trouble with my first set of Lee dies (380) right when I started reloading. It took me forever (and hundreds of THR PMs) to figure out that it was actually the die not sizing correctly instead of something I was doing, but sure enough Lee replaced the die body (IIRC) and ive had no tension troubles since.

 

[joneb]

Brass varies from brand to brand and lot to lot in no predictable way.

It varies in case wall thickness, volume, length and hardness or softness if you prefer. I keep mine sorted by head stamp and sort from there.

 

[GLOOB]

It varies in case wall thickness, volume, length and hardness or softness if you prefer. I keep mine sorted by head stamp and sort from there.

True. But if your sizing die is small enough, this shouldn't really matter. It's where the sizing die is a little loose that you lose neck tension on the thinner brass.

. Think you meant bigger, not smaller. In my experience, you need at least .002 to .003 for acceptable neck tension.

By measuring ID of the brass, right? I agree.

I find that I get plenty of neck tension in my pistol ammo with an expander that is up to the same size as the bullet. I found this surprising, at first, seeing as a standard expander is 2 mils smaller than a jacketed bullet and at least 3 mils smaller than a cast bullet. But in hindsight, the bullet itself, is going in the case. If an expander the exact same diameter is going to ruin neck tension, then there would be no way to get good neck tension, right? Neck tension comes from the spring back of the brass case. So an expander up to the same size as the bullet is only going to plastically deform the case as much as the bullet will, anyway. As long as the plug is no bigger than the minimum diameter of the bullet, the amount of elastic springback creating neck tension will be more or less the maximum amount. So anyhow, I aim my custom expanders to be less than a mil smaller than my cast bullets.

But to get this springback, the sizer has to get the brass at least maybe 2 or 3 mics smaller than bullet diameter, to begin with.

So 1 mil, or 2-3 mils, I agree with both answers, depending on what you are measuring. Case or expander. I have never sat down and meticulously measured it, but I would guess the case measures about 2 mils smaller than the expander ball after expanding, if the case was sufficiently sized to begin with.

 

[FMJBT]

I once had an older, out of spec dillon die that would not work on federal 9mm brass. Other brands would work.

The cases would seat, but you could spin the bullets with your finger.

After a call to dillon, we replaced the die and now it works on every brand of brass.

I've had out of spec does from multiple companies.

Best thing to do is if you have a friend that has a separate 9mm sizing die and take your troubled brass and use his/her die to reload your known, bad brass.

If it works fine, you know you have a die problem and not a brass problem.

 

[JamieC]

I'm using plated and FMJ with a dia. of .355. If I was loading lead at .356, the Blazer would probably be ok.

Yeah, I guess that extra thou is making the difference.

. Think you meant bigger, not smaller. In my experience, you need at least .002 to .003 for acceptable neck tension.

Yup, nothing proof reading might have fixed!

The 9mm is a high pressure round to begin with, so setback can lead to over pressure, particularly if you are at the upper end of the load range. Not trying to cause any unnecessary worry here, but it is something to test for and be aware of. Even with the Blazer brass I am having the "problem" with, I could probably load it and shoot it with no problems, assuming it only gets cycled once. But when it comes to reloading, I don't like relying on "probably" and assumptions.

I want to measure the P.D. bullets, just to double check. I agree, "probably and ASSumptions" ain't the way to go.

 

[Gadawg88]

I said I would follow-up once I got the Lee undersized die, so here it goes. It came yesterday and I only had a few minutes to work with it, but I believe it is going to solve my issue with poor neck tension with certain headstamps (Blazer, FC, Speer). I sized a couple each of those brands with the new undersized die and was getting an ID of .350 whereas before it was more like .354. Loaded a few and tested for setback using the bench press test and got no movement. I am not sure yet whether I will use it with all my brass or only the lose fitting brands. I loaded one RP case after sizing with the U die and it had a very pronounced coke bottle look. Much more than usual which is totally understandable given it was giving good neck tension when run through the normal die.

 

[LiveLife]

Good to hear you got your problem fixed. I followed this thread with interest as I have observed variations in the amount of resizing of brass depending on the brand of dies.

With 40S&W RCBS carbide dies, the resizing die does not resize as far down on the case as Lee carbide resizing die and cases resized with Lee die result with slightly smaller ID/OD at case mouth/case base.

I use Lee carbide resizing die for 9mm and do not experience the variations you mentioned on your OP for the majority of the various headstamp cases which are mixed range brass. Using different jacketed/plated/lead/coated bullets, I cannot push the bullet in pressed against the bench top and do not see significant bullet setback when fed from the magazine (with the exception of certain thinner walled cases).

Below is a picture of Berry's 124 gr RN in a case resized with Lee resizing die that clearly shows bulging of case neck showing good neck tension (blue arrows) and the "Coke bottle" look.

 

[GLOOB]

I don't think it is brand so much as individual dies. This why many folks suggested OP try an undersize die OR simply a new sizer.

My LEE 45 acp size die has the same problem. Mostly with RP brass.

 

[Walkalong]

I agree, order three sizers from the same company and your liable to get three different IDs on the carbide ring.

I have Redding and Lee 9MM sizers. They both give adequate neck tension, but the Lee is tapered and doesn't leave a bulge down low on the case like the Redding does. Both size the top of the case nearly identically.

I have four .45 ACP sizers, and they are all different. Two RCBS (Not even close), a Redding, and a Lyman. One RCBS is too big and won't size some cases (Mostly RP) sufficiently, one RCBS is very tight and leaves a pronounced coke bottle effect, The Redding tends to leave a ridge down low (They told me I was sizing wrong), although neck tension is decent, and the Lyman works great, excellent neck tension, barely a coke bottle look with some brass, and no ridge down low.

 

[LiveLife]

Interesting. I have three 9mm Lee die sets and also reloaded on multiple 9mm Lee dies (over the years I have helped set up several reloaders on Lee presses) and have not seen as big of a resizing issue as the OP.

With the tighter 40S&W Lone Wolf barrels, some resized brass with RCBS die would be snug in the chamber but Lee die would resize the same brass enough to rattle in the chamber.

I do realize that variations in machining could happen and my sampling is very limited.

 

[LiveLife]

I don't think it is brand so much as individual dies. This why many folks suggested OP try an undersize die OR simply a new sizer.

My LEE 45 acp size die has the same problem. Mostly with RP brass.

For me, it's been more caliber specific and headstamp related.

I have three Lee 45ACP die sets and both Lee and Dillon 45ACP resizing dies would have issues with the same particular headstamp cases with thinner walls but not to the point of OP or where I could push the bullet further in the case neck by pressing against the bench top, but measured in OAL reduction when fed/chambered from the magazine.

With 9mm, I did have particular problem with older "FC" headstamp cases and although I could not press the bullet in, the OAL reduction after being fed/chambered from the magazine was about .005" or more so I culled that lot of cases. The newer "F.C." headstamp cases do not have neck tension issues and I have noticed most newer cases have thicker case walls, including 40S&W cases.

I think this issue could be significant as some KaBoom threads have indicated below max and/or not a double charge was part of case failure/rupture. Poor neck tension could cause significant bullet setback which may significantly increase chamber pressure, especially for higher pressure 40S&W and 9mm.

 

[gamestalker]

I get the now and then piece that won't cooperate, but very far, and few between.

GS