irishlad
Contributing Member
I've been searching threads about loading 9mm and see the Lee 9mm U die mentioned quite a bit. Are there any negatives to using them over the standard Lee sizing die? Thanks.
Lee 9mm U Carbide Undersized Sizing Die
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CQB45ACP
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Good question. I use one so am interested in negatives.
JHTexas
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The benefits of the Lee undersized die would be most applicable to cases with thin walls, so that you can get the appropriate case tension, and not worry about bullet setback.
If you use these with thick wall cases, then you’re gonna really notice the extra effort to size the case and also the Coke bottle or wasp shaped cases after you seat the bullet.
Even though I use some of the thinner walled cases Blazer, F. C., Speer, I have never needed to use an undersize die.
If you use these with thick wall cases, then you’re gonna really notice the extra effort to size the case and also the Coke bottle or wasp shaped cases after you seat the bullet.
Even though I use some of the thinner walled cases Blazer, F. C., Speer, I have never needed to use an undersize die.
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JHTexas
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Here is a note from Dillon on theirs.
The thicker the brass, the more pronounced the coke bottle shape.
Some loaders really appreciate this because it prevents the possible bullet setback. The negative would be oversizing the cases that don’t need it.
The thicker the brass, the more pronounced the coke bottle shape.
Some loaders really appreciate this because it prevents the possible bullet setback. The negative would be oversizing the cases that don’t need it.
243winxb
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Thin walled brass may benefit from an Undersize die?
More important, does the fl die maintain the case taper. RCBS does. Lee may also? A long tapered insert is best.
Some brands of fl carbide ring dies may make the sized diameter 1 size , the whole length of the case. i think? Something to check.
Measure after sizing to know.
There are many different shapes & sized of 9mm Luger brass.
More important, does the fl die maintain the case taper. RCBS does. Lee may also? A long tapered insert is best.
Some brands of fl carbide ring dies may make the sized diameter 1 size , the whole length of the case. i think? Something to check.
Measure after sizing to know.
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JHTexas
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There have been changes in the industry on the carbide die designs over the last decade.
For example I mainly use Redding dies and they started with a single carbide ring that was about .150” tall. It tended to oversize the case base.
Then they offered a dual ring die to balance getting good neck tension and at the same time not over sizing the case base. Worked okay but you could still have apparent marks on the case because the carbide inserts were still straight, no taper.
Now they offer the NxGen dies that have a carbide insert that’s about .360” tall and tapered, does a nice job.
The Lee “U” die is Lee’s same design with the insert smaller in diameter by .002” to .003”.
For example I mainly use Redding dies and they started with a single carbide ring that was about .150” tall. It tended to oversize the case base.
Then they offered a dual ring die to balance getting good neck tension and at the same time not over sizing the case base. Worked okay but you could still have apparent marks on the case because the carbide inserts were still straight, no taper.
Now they offer the NxGen dies that have a carbide insert that’s about .360” tall and tapered, does a nice job.
The Lee “U” die is Lee’s same design with the insert smaller in diameter by .002” to .003”.
lightman
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I've loaded lots of 9mm and 45 and have never thought that I needed a special die. My carbide pistol dies are either Dillon or RCBS. Both seem to work fine.
runner3264
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Thin brass like Blazer and Winchester could use the U-die. Thicker brass like CBC won't. My Dillon won't size far enough on some of these cases so I run them through my U-die first. I noticed some setback when testing on these cases and bought the U-die. Usually cases with .010 wall thickness and larger will be okay.
Jonny2guns
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I've used the Lee 9mm carbide dies for the last 15 years and never had an issue with set back.... didn't realize it was a problem.
FWIW; I have reloaded thousands of 9mm with all different kinds of bullets, most in "once fired" brass (including many Blazer Brass and Winchester), for 5 different 9mm pistols, mostly with plain old Lee dies. Never had any chambering problems needing an undersize sizing die. I have heard of them, but never tried nor felt the need to try one...
CQB45ACP
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Lots of opinions that they’re unnecessary but no specific negatives! Has OP found chicken soup? You know, can’t hurt.
Zendude
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The only minor negative that I’ve found is that it takes more muscle to run cases through it, especially on my Lee Reloader press which has a relatively short arm.
CQB45ACP
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JHTexas
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I would say choose the right tool for the job. If your sizing die didn’t provide enough tension to keep the bullet from pushing back in the case then the Lee “U” die might be a good option. First know why it’s moving in the case. Maybe the expander is .001” too large in diameter.
If you’re using the logic that over sizing is better, then why stop with .003” less in diameter? Why not .010”?
Some reloaders like the thin walled brass because it sizes and expands with less effort. Using an undersized die takes some of that away.
The other thing to think about are tight barrel chambers for accuracy. Why allow cartridges to move around more in your expensive barrel.
Just a couple of thoughts…
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NMexJim
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Not needed. Standard dies will give you all the neck tension you need - thick brass or thin. I have quite a few 9mm including sub-compact. If I do my job, I don't get set-back. But, if you feel the need for more neck tension, go right ahead.
CQB45ACP
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Don’t know about OP but certainly nothing that’s been said would deter me from using one vs standard.
CQB45ACP
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Their description in the attached picture implies all of their dies are undersized. I must be incorrect? Couldn’t find this on their website.
I would say it says their dies size the cases sufficiently and here’s how you can tell.
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irishlad
Contributing Member
Thanks for all the replies and input. I'm gonna keep using the Lee standard one.
I love my standard Lee carbide 9MM sizer. It has a long tapered insert and does a great job.
I’ve tried one Lee undersized die and it was too tight, so I ended up with another standard sizer. That’s three sizers. Brand A which was too big, the U die, then brand C which worked well.
If I had called maker A they would likely have replaced it, but I wanted to try a brand C sizer anyway.
I’ve tried one Lee undersized die and it was too tight, so I ended up with another standard sizer. That’s three sizers. Brand A which was too big, the U die, then brand C which worked well.
If I had called maker A they would likely have replaced it, but I wanted to try a brand C sizer anyway.
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irishlad
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The other die that was mentioned alot when I was browsing 9mm threads on THR, was the Redding Competition Seater Die. I'm gonna get one soon, pricey but folks really like em.
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