Took the words right out of my mouth.

An actual hit?

So the expansion of brass cases is factored into, and part of the tuning of, many firearms cycling mechanisms. Dirty or smoked brass is often a sign of extraction timing problems. I've seen this problem with steel cased 9mm in a simple blowback carbine. Conversely, to demonstrate this, some semi autos in 7.62x39 don't shoot brass ammo well, tearing the cases with the extractor because they are designed for non-expanding steel cased ammo.

The concept sounds good, but I'll wait and see how it works in the real world. Brass pistol ammo is getting so cheap, I'm now only reloading some rifle ammo for accuracy.

Just because the case can take more pressure, doesn't mean the gun will function or be safe with more pressure. If that were the case, you would think this would already be applied to simple steel cased ammo that's been around a long time.

NOPE


if this stuff doesn't expand like brass, then have fun with all the extra cleaning and the lack of dependability you will get from your ARs... Your guns are going to get a whole HELL of a lot dirtier MUCH quicker. When the brass case expands upon round ignition, it essentially acts like a seal against the walls of the chamber, keeping a lot of the carbon, non-burned powder, etc. from blowing back into the action. This will essentially have the same effect as running common steel case ammo that we have now.

Yep, been running this stuff since December. Other than you need to run their sizing die with lube, no issues Can't wait for 223 and 308 NAS3 cases.

I assumed that it was engineered to temporarily expand sufficiently to seal the chamber... As a "given."
I'll have to read into the tests and specs.
Brass expands to seal the chamber, then contracts the millisecond after the pressure goes down as the bullet exits the muzzle, it just doesn't return all the way down to original size.
I'm assuming that this bunch of alloys do the same, but have less "creep" in length due to non-elastic deformation.

That was my understanding too. Elastic deformation vs plastic deformation.

Dude, are you really paying $40 for 1K of 9mm??? Go see Wes and get these for $20!!!
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It works exactly like a seal. A case has only two purposes. One is a transport medium for the ignition source (primer) propellant (powder) and bullet into the weapon's chamber. The second is to provide a positive seal to prevent the gases from leaking out of the rear of the chamber and hitting the shooter in the face. The most critical point is the neck. If it doesn't expand and seal, then crap comes back along the case making future chambering and extraction difficult.

My point (and I believe what mike was getting at too) was that I believe what they mean by "does not expand like brass" is not that it doesn't expand under pressures to create a seal but that it doesn't expand and experience a certain degree of plastic deformation like a brass case does. Instead I believe what it does is expand to seal the chamber and only deform elastically, which means it goes right back to the same shape/size it was before the pressure.