Lee 9mm undersize sizer die.

[parastoo]

Hi,
    Can one use this all the time instead of a normal sizing die?
Thanks,
           Mark

[Crawl]

Yes.

When I switched to the Undersized 9mm sizing die only (100% of the time), my rounds started fitting in the Hundo case gauage FAR more frequently. But plenty of people get by without it.

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[SoCal]

I use mine all the time.  I still get the occasional case that doesn't fit all the way into a case checker (I check every case) but much less often, maybe 1 in a couple 100 with random range brass. 

[bang bang]

welcome,

yes you can.

but consider this.

you are "working" the brass everytime you re-size.  So under sizing only works it more.

how much it will affect the life of the brass is the question.

[SI VIS PACEM PARRABELLUM]

welcome,

yes you can.

but consider this.

you are "working" the brass everytime you re-size.  So under sizing only works it more.

how much it will affect the life of the brass is the question.

Been using mine full time for several years and haven't run into any issues with brass failing any sooner than using the standard size die. Every time you fire a round the case gets worked too so there's that.

[TjB101]

Ditto ... I use the U die all the time.  Not sure where the std one that came with the set is located.  [emoji853]

[Crawl]

I'd much rather incrementally overwork the brass than have dozens or hundreds of rounds that won't go into the case gauge.

That being said, I also use a Factory Crimp Die, and that probably helped more than anything else.

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[lewmed]

 I use my U-die when ever I load mixed range brass to avoid bullet set back and have done so for many years with no issues.

[bang bang]

Dont know what you all are doing or buying your stuff, but i have yet to have a round not go into a chamber, other than some 223 i had loaded for a friends Kimber way back then.

but for my CF handguns, all of them have worked with the exception of CZs with the short chamber.

[SI VIS PACEM PARRABELLUM]

I've never had a single issue chambering a round and that was not why I went for the U die. Several years ago I ran into some thin cases that had no neck tension after resizing. These cases were thin enough that you could seat a bullet in the case mouth and force it all the way into the cases by holding the round between the thumb and forefinger and this was before any flare was added to the case. The U die completely cured that.
Another benefit to the U dies is when it's properly adjusted it will size the case all the way down which is important when you are loading cases fired from these wonderful modern striker fired pistols that DO NOT have fully supported chambers like the Sig P320. I owned a couple P320's briefly and they both put a real nice bell right at the base of the case. The U die smooths that right out.

[Crawl]

Don't know if have had one not chamber because I run every round through a case gauge. It's the gauge that I want them to fit.

Also, the base of many cases are quite swollen because they are mostly running through chambers with unsupported chambers.

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[Fuzzy Sights]

Use my u die constantly.  Got way to many failures to feed without it.  Have even used one in between my seating and crimp die on match ammo.  Got excellent results.

Good luck.

JW

[Bret]

Dont know what you all are doing or buying your stuff, but i have yet to have a round not go into a chamber, other than some 223 i had loaded for a friends Kimber way back then.

but for my CF handguns, all of them have worked with the exception of CZs with the short chamber.

Same here.  So many people needing undersized sizing dies seems odd to me.  It might be that my Hornady sizing die sizes cases down more than is typical.  I did have an issue with my 40S&W Hornady sizing die not providing some case/bullet combinations enough tension.  I ended up purchasing a Redding sizing die to solve the issue.  I now use the Redding die for all my 40S&W sizing.

[lewmed]

 I'm Like reply #9 if you run enough mixed headstamp brass you will find what I call oddball brass extra thick cases are not much of an issue but thin cases will let the bullet slip back into the case. I don't have many problems with US made brass Federal, Remington, Winchester, Speer and CCI Blazer but mix in a few imported cases and my Dillon 650 and 750 will start to choke you can feel it when the case is being sized and primed. That is when I start seeing loose bullets and bullet setback and even high primers the U-die will fix those issues. With the 2020 and 2021 shortages I've been hand sorting my brass by headstamp I wait until I have a couple thousand then swage the primer pockets and run all the oddball and imported brass through my U-die.

[Bret]

Good point lewmed.  I keep my brass sorted, so perhaps that's why I have not encountered this issue.