9mm "undersized die, WTH

I am assisting a friend who inherited all his dad's reloading stuff. No dies are carbide. In searching for new and used stuff on various sites, I came across this 9mm undersized unit. It's carbide, but claims to undersize the case to insure reliable stripping from mags.I could see squeezing the base down a bit, but why the case mouth, it's already to the point one squeezes down cast boolits a bit more than we'd like to see. Is this the way to go now? Just as well get it for him if that is the prevailing wisdom.

Mayhaps it is to remove "case bulge" at the base of the case, or possibly it would be considered to a type of "small base" die for autoloaders? I have no idea why why one would need to size the case mouth smaller unless you had a very tight chamber and barrel. Good luck with your new reloading friend.

Could be for ammunition used in a blow back carbine?

ACC

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Originally Posted by ACC

Could be for ammunition used in a blow back carbine?

ACC

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Aren't all pistols blowback? Asking for a friend of course. Carbine, pistol, potayto, potawto

I got one of these dies in a deal, no idea what it would be used for. Making a die with the carbide ring set lower to size closer to the base might be useful, but I’m not so sure that these aren’t just regular sizing dies that failed inspection and got stamped “U” and I can’t think of a use for them.

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Originally Posted by JimB..

I got one of these dies in a deal, no idea what it would be used for. Making a die with the carbide ring set lower to size closer to the base might be useful, but I’m not so sure that these aren’t just regular sizing dies that failed inspection and got stamped “U” and I can’t think of a use for them.

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My original thoughts too

EGW marketed an undersized die in both 40 S&W, and 9mm. They were specially made by Lee, expressly for EGW.

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Originally Posted by gbertolet

egw marketed an undersized die in both 40 s&w, and 9mm. They were specially made by lee, expressly for egw.

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egw


???????

OK, I found EGW gun parts, but they don't really state the reason for he undersize die.

Here is what EGW says:
“EGW offers custom designed, carbide sizing dies that are 0.003" smaller in diameter than typical dies.
Not only is it smaller in diameter, but the bottom corner is also radiused which sizes the case further down.
This helps prevent feed failures from cases that bulged near the base during reloading- which is typical of brass fired in loose chambered guns.”

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Originally Posted by la5676

Aren't all pistols blowback? Asking for a friend of course. Carbine, pistol, potayto, potawto

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No. Most 9mm and up pistols are delayed recoil from a locked breech.
https://en.wikipedia.org/wiki/Recoil_operation

Blowback are not locked and rely on the mass of the bolt and buffer or slide and spring to slow action/bolt speed.
https://en.wikipedia.org/wiki/Blowback_(firearms)

How it applies is that the brass can be moving rearward in a blowback operated gun as the powder is still igniting leading to brass being bulged due to being outside the chamber--no chamber support.

Here are a few from my AR9. It does this to ~1/20. I need to check to see if I'm getting bullet setback vs needing more buffer weight.

https://i.imgur.com/8o60kuL.jpg

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Originally Posted by la5676

I am assisting a friend who inherited all his dad's reloading stuff. No dies are carbide. In searching for new and used stuff on various sites, I came across this 9mm undersized unit. It's carbide, but claims to undersize the case to insure reliable stripping from mags.I could see squeezing the base down a bit, but why the case mouth, it's already to the point one squeezes down cast boolits a bit more than we'd like to see. Is this the way to go now? Just as well get it for him if that is the prevailing wisdom.

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It is NOT for cast boolits but rather for the undersized J-word projectiles ...
Actually any 9mm boolit , cast -plated or whatever that is .355" or .356" diameter , could probably use a undersized sizer .
I size my cast boolits .357" to get them to work in my regular steel dies ...
.355" and .356" projectiles just fall into my resized 9mm necks .
If you cast and coat your boolits ... you don't need a undersized sizer ...you need a good neck/case expander to get the coated boolits in the case undamaged .

My advice ...buy the undersized sizer only if loading .355"-.356" projectiles and your regular sizer wont size the case down enough to hold the boolit firmly .
Neck tension is important to have and boolit/bullet size will indicate what die is necessary .
Gary

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Originally Posted by gwpercle

It is NOT for cast boolits but rather for the undersized J-word projectiles ...
Actually any 9mm boolit , cast -plated or whatever that is .355" or .356" diameter , could probably use a undersized sizer .
I size my cast boolits .357" to get them to work in my regular steel dies ...
.355" and .356" projectiles just fall into my resized 9mm necks .
If you cast and coat your boolits ... you don't need a undersized sizer ...you need a good neck/case expander to get the coated boolits in the case undamaged .

My advice ...buy the undersized sizer only if loading .355"-.356" projectiles and your regular sizer wont size the case down enough to hold the boolit firmly .
Neck tension is important to have and boolit/bullet size will indicate what die is necessary .
Gary

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That was exactly the reasoning I was wanting to hear. I cast, coat, and size most everything to .358, and encouraging him to also. I have sold all my lube sizers anyway.

Thanks

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Originally Posted by la5676

I am assisting a friend who inherited all his dad's reloading stuff. No dies are carbide. In searching for new and used stuff on various sites, I came across this 9mm undersized unit. It's carbide, but claims to undersize the case to insure reliable stripping from mags.I could see squeezing the base down a bit, but why the case mouth, it's already to the point one squeezes down cast boolits a bit more than we'd like to see. Is this the way to go now? Just as well get it for him if that is the prevailing wisdom.

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I’ve been handloading since the early 80’s but never bothered with 9mm because it was such a pain to retrieve brass so I sold my S&W model 39(big regret) and only shot my .41 mag up until about 15 years ago when I added a couple .38sp, .357mag, and several 9mm’s. So when I finally started loading for 9mm I had a few problems since it’s quite different than straight wall revolver cartridges. I won’t go into all my trials and tribulations but basically once I started using an undersized sizing die all my problems disappeared. But, I don’t shoot lead in my 9mm’s, strictly copper plated so them being undersized a bit wasn’t a problem. Just lately I’ve added the NOE powder through expanders to my regimen and I bet they would eliminate any undersized case mouth problems since you can get them in the proper size not to swage a cast bullet and they are implemented post sizing. The only issue with these expanders is they’re only designed to work with Lee powder through dies, for me it’s not an issue since all my pistol reloading is done using the Pro Auto Disc powder measure.

I had the bright idea to buy some 90 gr jacketed hollow points to load some screaming 9mm. Those things were so short I couldn't get enough neck tension to hang onto them with "thin walled brass". I bought a Lee "U" die and it seemed to solve the problem. YMMV

You'll find the small base dies for several popular cartridges, including .223, .308, 9mm, .45 ACP, etc. I've got one for .45 ACP (all of those mentioned, actually...) and its main function is in ironing out the bulge near the base of cases fired in Glocks and recovered from the range. It does a good job, but one need a sturdy, solidly mounted press like a Rockchucker and even then it requires a lot of effort on the handle. You'll need to then run the cases through a neck/mouth expander before attempting to seat the new bullet. You may then see a slight bulge where the base of the new bullet is located inside the case, but as long as it will pass in and out of a Lee Carbide Factory Crimp die you're good to go.

DG

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Originally Posted by la5676

Aren't all pistols blowback? Asking for a friend of course. Carbine, pistol, potayto, potawto

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No, not all of them. In fact, not even most of them.
There ARE blowback pistols in many major pistol calibers, but the majority of pistols use a locking system of some sort to prevent the action from opening until chamber pressures have dropped well below their peak. This is in contrast to blowback actions, which use only the recoil spring tension and the bolt mass to resist the highest chamber pressures generated by the round.
If memory serves, the inexpensive but remarkably effective Hi-Point pistols are blowback actions, but they're the only ones I can name, off the top of my head. Conversely, I think the majority of Pistol-Caliber Carbines (PCCs) currently available operate on blow-back actions. The only exception that I can think of is the SIG MPX in 9mm.

As for the use of a sizing die that sizes the cases too small at the case mouth, I can think of no real reason for it. I guess it COULD be to provide extra friction between case and projectile when loading base-jacketed projectiles, but that is all I can come up with. If the die IS a reject, a bit of polishing in the case neck area might make it less troublesome.

Don't forget the Astra pistols....400, 600/43....blowbacks in 9mm Largo and Luger.

DG

Most .380's and lower power centerfire autos are blowback. It takes too much slide weight to slow the slide speed of larger calibers down. That's why Hi-point has such a huge slide on theirs--made of zinc to save on cost.

Actually my 380 Astra(star) was like a 1911.

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Originally Posted by popper

Actually my 380 Astra(star) was like a 1911.

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It is better if they are. Less recoil spring to overcome when chambering. I've always felt my wife's blowback Bersa was ridiculous because of the high effort required to chamber a round. That type of gun is intended for someone recoil sensitive who may not be super strong and it has just about as much recoil as a regular locked breech gun and is hard to work the slide.

There may be something more to this; my supposedly standard Lee 9mm sizing die, under-sizes cases, with every loaded round having a bulge for the seated length of the projectile. The ammo chambers and fires perfectly in all manner of pistols, but it still irks me a bit.

My Lee 9mm undersizes, too. This and 40SW are the only calibers I really have to use an oversize expander die for cast bullets. Everything else barely gets adequate neck tension, so cast bullets will seat fine with just a mouth flare.

My Lee 223 and 45ACP are bordering too loose, neckwise. Just good enough for 99% of my brass, but some random cases are too thin to get adequate tension.

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Originally Posted by la5676

I am assisting a friend who inherited all his dad's reloading stuff. No dies are carbide. In searching for new and used stuff on various sites, I came across this 9mm undersized unit. It's carbide, but claims to undersize the case to insure reliable stripping from mags.I could see squeezing the base down a bit, but why the case mouth, it's already to the point one squeezes down cast boolits a bit more than we'd like to see. Is this the way to go now? Just as well get it for him if that is the prevailing wisdom.

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I don't see how a carbide 9mm would oversize the case mouth, the 9mm is tapered, if it oversized the case mouth it would really oversize the base. Even if it oversized the case mouth the expander would set the mouth back to the right diameter. Your case mouth opening is set by the expander not the sizer. If you have a problem with cast bullets being squeezed too much get a proper diameter expander. I like Lyman M dies for this as you have easily replaceable expanders.

Tim

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Originally Posted by gloob

.....My Lee 223 and 45ACP are bordering too loose, neckwise. Just good enough for 99% of my brass, but some random cases are too thin to get adequate tension.

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That is not great but you say borderline so maybe if the die sets come with a taper crimp die, that would make workable ammo.

Tim

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Originally Posted by HumptyDumpty

There may be something more to this; my supposedly standard Lee 9mm sizing die, under-sizes cases, with every loaded round having a bulge for the seated length of the projectile. The ammo chambers and fires perfectly in all manner of pistols, but it still irks me a bit.

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If these are standard dies, you need to back them out a bit. Do not run them all the way down to the shell holder. The 9mm case is tapered so not pushing them into the die as far should cause them to size less. That should fix your problem.

Tim

RCBS dies is all thats needed. Sizes the taper into the case. Comes with an "M" type expander. Taper crimps.

Photos- https://www.thehighroad.org/index.ph...9mm-luger.317/

I had a full auto MAC 10 in 9mm that might have liked this die.
Can't test theory on it now as it went hunting pirates in the Caribbean.