9mm "undersized die, WTH

[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.

[gloob]

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.

[dtknowles]

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.

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

[dtknowles]

.....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.

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

[dtknowles]

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.

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

[243winxb]

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/

[kywoodwrkr]

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.