Look what I found in the "Mix".

[Nevada Ed]

Was messing around in the reloading room, just checking my bullets on hand
and decided to get some 9mm cases ready and to check them out
for any defects and if they were good to go, and place in a Zip-lok bag.

Low and behold look what I found, and three of the little rascal's.
I will use them for future "Dummy rounds" but was surprised to find them
and glad that I did.

I just don't need any surprises, at my age.
I was also amazed at how dirty the primer area and inside the case was.
Must be pre-historic, Unique ?

Stay safe, everyone.

 

[BC38]

I've seen a couple of those. Seems like I read two different theories.
1) It reduces the interior volume of the case to generate more pressure with less powder.
or
2) The reduced inside diameter provides a "stop" to prevent bullet setback.

 

[robertrwalsh]

I am guessing on door #2, but that is only a guess.

 

[Duckford]

I think the stated idea was that it stopped bullet setback, used by places like Freedom Munitions.

My pictures of the cases separating in half at the mark in my Uzi ran around here for a while. I'll have to find them again.

I had quite a few problems with those cases in my Uzi until I just plain quit using the ones I bought.

 

[BC38]

I think the stated idea was that it stopped bullet setback, used by places like Freedom Munitions.

My pictures of the cases separating in half at the mark in my Uzi ran around here for a while. I'll have to find them again.

I had quite a few problems with those cases in my Uzi until I just plain quit using the ones I bought.

Interesting. Does the Uzi have a larger than normal chamber diameter? Or is there something else about it that leads to these cases separating at the "step"?

 

[Duckford]

Interesting. Does the Uzi have a larger than normal chamber diameter? Or is there something else about it that leads to these cases separating at the "step"?

The barrel screws in and out awfully easy, and you can tell it has the slightest of slop in it. I'm going to guess the headspace is probably pretty loose, and the more open tolerance might be the source of the issue.

I remember a while back someone else had the same problem, but with a handgun. Not sure what his issue was, but it seems like there can be case separation with any type of less than tight spec weapon.

 

[RWJ]

Interesting. Does the Uzi have a larger than normal chamber diameter? Or is there something else about it that leads to these cases separating at the "step"?

It's been a while since I dealt with them, but my guess would be its blow-back only action, relying on the bolt's weight and recoil spring. Perhaps a weakened spring?

 

[Duckford]

It's been a while since I dealt with them, but my guess would be its blow-back only action, relying on the bolt's weight and recoil spring. Perhaps a weakened spring?

The rifle was new from Century, but assembled by them out of parts kits that were imported. Not sure what parts they put in to get the whole import/domestic part count correct. Spring didn't seem weak, and I'm pretty sure I've never put more than 2,000 rounds through it.

Maybe I should look into getting some headspace gauges and giving it a thorough look.

 

[BC38]

The barrel screws in and out awfully easy, and you can tell it has the slightest of slop in it. I'm going to guess the headspace is probably pretty loose, and the more open tolerance might be the source of the issue.

I remember a while back someone else had the same problem, but with a handgun. Not sure what his issue was, but it seems like there can be case separation with any type of less than tight spec weapon.

That is the most logical explanation I can think of. An out of spec chamber would allow the brass to expand beyond it's elasticity limits and the thinner section would obviously expand the most. The sharp edge of the step would concentrate the stress and cause a fracture line right at the step.

 

[Nevada Ed]

I've seen a couple of those. Seems like I read two different theories.
1) It reduces the interior volume of the case to generate more pressure with less powder.
or
2) The reduced inside diameter provides a "stop" to prevent bullet setback.

I measured how deep that "Step" was inside my cases.
It was +/- .37".

I can only seat my Berry 147 plated RN about .30" before the case starts to bulge
with some of the "Mixed" brass that I use.

I don't know why it is there or the companies reasoning for this design.

A 147 Berry RN set this deep would put the case rim, past the bullet's wall and into the Ogive area.

 

[DWalt]

I am unfamiliar with that case design. I suppose that one possibility is that the case wall is thickened near the base to add extra strength to prevent case blowout of high pressure loads when used in pistols having barrels with unsupported chambers. That was the idea behind the now-defunct 9x23 Winchester case.