When should you use and Undersize sizing die?

[AbitNutz]

I've read a couple of posts of people using EGW's undersize sizing die. To be honest, I've never heard of these. I shoot a 1911 (mostly) with a fully ramped barrel. Am I to assume that these kind of dies are used mainly in guns that overly distort fired brass. Or is the purpose to make the round chamber more easily? 

If anyone can share the full reasoning behind these dies I'd appreciate it. 

[Scott Steele]

If reloading range brass it's a good way to make sure the round will go into battery. Its insurance. It's also best to chamber check the rounds with the actual pistol barrel chamber used.
Most malfunctions I see are due to poor quality control on reloaded ammo.
I use a U die for 9mm, 40 S&W and 45 ACP. It also aids in preventing bullet set back in .40.
If my reloaded ammo can fall into the barrel chamber and fall out then it's good.


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[Hi-Power Jack]

2 minutes ago, Scott Steele said:

a U die  aids in preventing bullet set back in .40.
If my reloaded ammo can fall into the barrel chamber and fall out then it's good.

I don't use a U die - I just chamber check my ammo.  I usually find

Very Few rounds that will Not chamber check.

BUT, IFF I loaded .40 major, with heavy bullets and fast powders

(which is what I'd use for .40 Major), I'd invest in a U-die.    

[AbitNutz]

The "U" die is starting to sound like a good idea and may fall into the catagory of "why not?".

[MemphisMechanic]

I have a friend who swears by having a Dillon resize / decap in station 1 and a U-die in #2 on his 650. Obviously, you lose the ability to run Dillon's powder check in #4 when you do this.

I use a standard Lee sizing die (the "non U" flavor) on a 650 and I'm quite happy with it.

Edited October 17, 2016 by MemphisMechanic

[IHAVEGAS]

4 minutes ago, AbitNutz said:

The "U" die is starting to sound like a good idea and may fall into the catagory of "why not?".

It costs money, works the brass more, works your arm more and doesn't make any difference for 99% of reloaders.

But if you want it  or need it, great!

 

[AbitNutz]

51 minutes ago, IHAVEGAS said:

It costs money, works the brass more, works your arm more and doesn't make any difference for 99% of reloaders.

But if you want it  or need it, great!

 

Ohh...that's a jaded reply..lol. Seen too many "next best thing to sliced bread" have we? That's why I ask. I don't seem to be having any such issue and I'm wondering where this all comes from. I run a 1911 with a Kart barrel with a C/P ramp that supports the case as well as it can be supported. The chamber is tight but I don't have any malfunction issues. So where does this need for a U-die come from? 

[Hi-Power Jack]

1 hour ago, IHAVEGAS said:

It costs money, works the brass more, works your arm more and doesn't make any difference for 99% of reloaders.

+1.

[AbitNutz]

One of the complaints I've seen about not being able to handle a mild misalignment and the case getting mangled/crushed.

[AzShooter]

I've noticed I get more cracked brass faster after using a U-die.  I'm going back to my Dillon.

 

[AbitNutz]

I'm still kinda not understanding what purpose they serve. Are they the pistol equivalent of small base dies for rifles? As I said, this is the first I've heard of them...I shoot really high pressure loads and never ran into a situation where a almost any straight walled pistol sizer didn't work. What's the point of making them smaller than factory spec? What gun/barrel needs this kind of attention?

[rooster]

Probably not worth it in 45 acp.  If you resize brass that comes out of a loose chambered gun such as a glock, and want to use that brass in a tight match chamber then you'll be glad you got the "u" die.  I put a Barsto barrel in my g34 and at least 50% would not chamber flush with the barrel hood.  Went to the u die no more problems.  If your shooting a loose chambered gun then not worth it because you regular die will work just fine.

[RiggerJJ]

I use em for setback prevention in 9, 40, and 45. 45 needed it the most for me. Ill bet that most who don't use em should because of setback...

And I use a rollsizer before loading...

jmho

jj

Edited October 17, 2016 by RiggerJJ

[GregJ]

When I started shooting USPSA and reloading 45ACP for SS, I had a heck of time with bullet setback.  I tried all sorts of things, including separating out headstamps and use the better ones for larger matches.  The EGW-U die solved all my setback issues.  I have been using it for several years now with no issues.

[Scott Steele]

I roll size as well before u die.



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[Scott Steele]

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[AbitNutz]

So the U-size die pretty much keeps the bullet from being pushed back in the case? I haven't run into that particular problem. What is the principle cause of that in 45 acp? Before the u-size die were people just roll crimping it? 

[rooster]

The u die resizes the case to just in front of the extractor groove.  The taper crimp die is what prevents setback.  9,40,45 all head space at the mouth.  Crimp should be bullet dia. + 2x case wall thickness or a little less.  If your getting setback it is not because of the lack of a u die.  You should not roll crimp rounds that head space on the case mouth.

[IHAVEGAS]

It is interesting to think about.

The only time I have see setback is with dummy rounds that I use for slide lock reload practice. After many operations the dummy's all setback but I have never seen the problem with dummy (or live) rounds that were not chambered several times. 

Bullet choice (hardness, shape, diameter), particular gun/magazine geometry, and recoil spring force would seem likely to play a part. Tapered brass (9mm) vs straight walled brass would also seem likely to have some effect.

 

[AbitNutz]

Boy, this is confusing. We have anecdotal evidence that the U-die prevents bullet set back. I'm lost about the true reason to use one of these. There must be something to using a U-die as their use seems to be spreading. It wouldn't surprise me if RCBS, Redding, etc start making U-dies. 

[RDA]

9 hours ago, AbitNutz said:

Boy, this is confusing. We have anecdotal evidence that the U-die prevents bullet set back. I'm lost about the true reason to use one of these. There must be something to using a U-die as their use seems to be spreading. It wouldn't surprise me if RCBS, Redding, etc start making U-dies. 

It shouldn't be that confusing.  The Undersizer die is 0.001" smaller in diameter than typical dies and the bottom edge of the die is radiused which sizes the case further down. The die is good to use if you have a tight chamber or experience cases that are bulged near the base.  If you don't have these issues, there is really no reason to use the die as it works the brass, your equipment and you more.

[Sarge]

14 hours ago, rooster said:

 The taper crimp die is what prevents setback.

 If your getting setback it is not because of the lack of a u die.  

Your first comment is just not true. Case sizing prevents setback not crimp. If a case is sized right a bullet won't setback even if you don't crimp it. The tight sizer die creates good neck tension which is what holds the bullet in place. The crimp just flattens out the flare. As a matter of fact too many ch crimp can actually reduce neck tension.

As to the 2nd point, not running a udie can indeed lead to setback. 

I had setback when using a Dillon sizer. But only with certain components. MG bullets and FC BRASS were the worst. Thin case walls, slick HARD bullet, and a Dillon sizer added up to not enough neck tension.

The only time I'd agree that crimp holds a bullet is in a situation where cannalured bullets are used in roll crimped applications

[TONY BARONE]

Have been using a u die for years and it is the best method for preventing bullet set back. Set back can be a real hazard.

[ThePeanutGallery]

I was having some serious setback issues with Speer and *FC* stamped brass in 9mm, to the point of just being able to squeeze a bullet all the way into a case by hand.  I switched to the EGW U die and haven't had an issue since.  Was well worth the minor added effort to know I wasn't going to end up making little grenades out of my reloads.

[AbitNutz]

I like the idea of avoiding bullet set back every way possible. I shoot a lot of 45 Super level loads and any set back at all of the bullet could turn the cartridge into a fine grenade.