Lee 9mm U Carbide Undersized Sizing Die

[CQB45ACP]

I would say it says their dies size the cases sufficiently and here’s how you can tell.

But that’s not what it says—it begins:

“Dillon Precision Carbide Sizing Dies contain a long, tapered, insert that sizes the case down further than standard dies.”

 

[CQB45ACP]

They are very nice, and if you shoot multiple bullets you can just dial back and forth.

But, like the undersized die, it’s unnecessary (and I have two of them)

 

[CQB45ACP]

Here are 15 9mm rounds assembled this AM.

All sized using a Lee undersized sizing die—Providing insurance against set back through increased tension.

Then carefully expanded but not flared using a Lee old style PTX.

Then seated using a Redding competition micrometer adjusting seating die.

None are crimped—none needed it. Since we know taper crimping does nothing against set back.

And polished to jewelry-like shine.

 

[irishlad]

They are very nice, and if you shoot multiple bullets you can just dial back and forth.

+ they look cool

 

[Jim Watson]

But that’s not what it says—it begins:

“Dillon Precision Carbide Sizing Dies contain a long, tapered, insert that sizes the case down further than standard dies.”

Balderdash. They can't sized down any farther than the depth of the shell plate allows. And not even that because they have a lot of radius on the mouth so the case in the floppy shell plate will align better.

I am using the U die now because I am loading 115 gr plated bullets which are seated shallowly and it takes a lot of sizing to get adequate bullet pull. I use the Dillon sizing die if loading heavier bullets with more bearing surface and deeper seating.

 

[Walkalong]

But that’s not what it says—it begins:

“Dillon Precision Carbide Sizing Dies contain a long, tapered, insert that sizes the case down further than standard dies.”

Ah, missed that, yep, they are supposedly cut to minimum chamber dimensions. Dunno.

Lee supposedly does as well, which would put their U die even tighter

 

[Walkalong]

Balderdash. They can't sized down any farther than the depth of the shell plate allows. And not even that because they have a lot of radius on the mouth so the case in the floppy shell plate will align better.

Correct, the radius on any sizer determines how far down the case it can size.

Tighter is another discussion.

 

[CQB45ACP]

Balderdash. They can't sized down any farther than the depth of the shell plate allows. And not even that because they have a lot of radius on the mouth so the case in the floppy shell plate will align better.

I am using the U die now because I am loading 115 gr plated bullets which are seated shallowly and it takes a lot of sizing to get adequate bullet pull. I use the Dillon sizing die if loading heavier bullets with more bearing surface and deeper seating.

I haven’t a clue but don’t shoot the messenger

Maybe it’s AI generated misinformation?

 

[CQB45ACP]

+ they look cool

I have said that exact thing over and over and posted pictures—it’s cool looking and I still want a micrometer adjusting expander to complete my set.

 

[Jim Watson]

Ah, missed that, yep, they are supposedly cut to minimum chamber dimensions. Dunno.

Lee supposedly does as well, which would put their U die even tighter

Minimum CHAMBER dimensions? No wonder I was getting setback from short slick bullets. I want minimum or at least mid-spec CARTRIDGE dimensions.

 

[KY DAN]

I have bith 9mm and 45 acp Undersized dies.

The only negative I can find is there is more resistance seating bullets and flaring the cases with a lyman m die.

I have discontinued their use, I never had an issue using a standard lee sizer in these calibers I was just persuaded by a John Taffin article during covid 19 to try them

 

[Walkalong]

Minimum CHAMBER dimensions? No

No, my bad

 

[Soonerpesek]

Balderdash. They can't sized down any farther than the depth of the shell plate allows. And not even that because they have a lot of radius on the mouth so the case in the floppy shell plate will align better.

I think the meaning they are trying to get across is that the die sizes the case down FURTHER———not FARTHER…
Meaning the dimension is smaller than the standard die, not that the die reaches farther down to the base…..
Comprehension is fundamental…

 

[Jim Watson]

Could be what they are advertising.
I can definitely say it is not enough for good bullet pull with my combination of components, that takes the "U" die.

 

[CQB45ACP]

Could be what they are advertising.
I can definitely say it is not enough for good bullet pull with my combination of components, that takes the "U" die.

Excuse my ignorance but what’s bullet “pull”?

 

[JHTexas]

Excuse my ignorance but what’s bullet “pull”?

It’s a way of testing how much case tension or hold it has on the bullet

 

[CQB45ACP]

It’s a way of testing how much case tension or hold it has on the bullet

How does a layperson like me do that? I’d like to see if I’m simply deceiving myself using the undersized dies.

 

[JHTexas]

How does a layperson like me do that? I’d like to see if I’m simply deceiving myself using the undersized dies.

You would use a bullet puller on the press and compare the effort to other known loads with adequate case tension.
The other way is to use a impact bullet puller and repeat with the same energy on a known round.
These are somewhat subjective but I’ve used them and been able to find a difference in case hold on the bullet.

 

[CQB45ACP]

You would use a bullet puller on the press and compare the effort to other known loads with adequate case tension.
The other way is to use a impact bullet puller and repeat with the same energy on a known round.
These are somewhat subjective but I’ve used them and been able to find a difference in case hold on the bullet.

Okay

I’ve used the latter and can say in 45acp anyway it’s at least a couple more whacks with undersized die.

I’ll try it again with some dummy rounds paying closer attention.

Haven’t tried 9mm nor collet puller which I don’t like anyway.

 

[JHTexas]

It is very probable that you are not getting more neck tension by using the Lee “U” die with thin walled brass.
What you are probably getting by using the Lee “U” die results in having the case smaller in diameter underneath the heel of the bullet.
That is the Coke Bottle shape that it creates. That puts a restriction underneath the bullet heel and helps prevent the bullet from setting back.
Dillon states their dies prevent bullet set back. I think it is mainly achieved by the narrowing of the case diameter under the bullet heal.

 

[JHTexas]

Okay

I’ve used the latter and can say in 45acp anyway it’s at least a couple more whacks with undersized die.

I’ll try it again with some dummy rounds paying closer attention.

Haven’t tried 9mm nor collet puller which I don’t like anyway.

What brand of cases are you working with?

 

[Jim Watson]

Bullet pull is measured with an instrumented bullet puller. Mostly a mil-spec, the requirement is pretty high. I don't think the commercial manufacturers bother, too many reports of setback of factory loads.

Whacks with an inertia puller is a rough measure. I had a duff round to pull the other day and it did not take a lot, but more than required to separate one that had set back.
I think pushing the bullet against the bench edge tells the reloader where he is.

Perhaps the constriction contributes, I have a die that puts a cannelure in a 45 case at the base of the bullet, like a few factory loads still do. That sucker is not setting back.

 

[CQB45ACP]

What brand of cases are you working with?

Any and all but I separate

For the time being I’m in a just Winchester rotation of 200ish to see how long they last.

 

[CQB45ACP]

Bullet pull is measured with an instrumented bullet puller. Mostly a mil-spec, the requirement is pretty high. I don't think the commercial manufacturers bother, too many reports of setback of factory loads.

Whacks with an inertia puller is a rough measure. I had a duff round to pull the other day and it did not take a lot, but more than required to separate one that had set back.
I think pushing the bullet against the bench edge tells the reloader where he is.

Perhaps the constriction contributes, I have a die that puts a cannelure in a 45 case at the base of the bullet, like a few factory loads still do. That sucker is not setting back.

I’ve never had a push against the bench move a bullet but quite a while back I did some dummies in a 1911–holy cow.

 

[JHTexas]

Bullet pull is measured with an instrumented bullet puller. Mostly a mil-spec, the requirement is pretty high. I don't think the commercial manufacturers bother, too many reports of setback of factory loads.

Whacks with an inertia puller is a rough measure. I had a duff round to pull the other day and it did not take a lot, but more than required to separate one that had set back.
I think pushing the bullet against the bench edge tells the reloader where he is.

Perhaps the constriction contributes, I have a die that puts a cannelure in a 45 case at the base of the bullet, like a few factory loads still do. That sucker is not setting back.

I’m glad you mentioned a case cannelure. The “U” die creates the reverse taper seen after the bullet is seated creating a lesser but type of restriction like a cannelure.

This picture shows the reverse taper past the bullet heel: