I bought a batch of 300 Blackout range brass a while back and I am now just going through it. In the first 200 rounds of processing, I came across 3 of these cases. All of them different headstamps and all 3 headstamped as 300 Blackout.

looks like somebody stuck the chamber reamer in an extra 3/16 inch deeper into the barrel.

looks like somebody stuck the chamber reamer in an extra 3/16 inch deeper into the barrel.

This is what I learned. Some firearms have a stepped chamber. I Googled it and apparently it is more prevalent in handgun cartridges like 9mm. But it is a thing.

I learn more and more every day.

I know what your talking about with 9mm. My VP9 does that. The step is only .006in on the fired brass.

I also found some thing about 7.62x39 fired brass with stepped neck on ar15.com https://www.ar15.com/forums/armory/stepped_necks_in_7_62x39_cases/42-411445/
someone stated "The step in the chamber neck is to identify fired cases as coming from a civilian rifle and not from an unregistered military rifle. This is the law in Russia."

I don't believe that's whats going on with your 300BLK brass.

I know what your talking about with 9mm. My VP9 does that. The step is only .006in on the fired brass.

I also found some thing about 7.62x39 fired brass with stepped neck on ar15.com https://www.ar15.com/forums/armory/stepped_necks_in_7_62x39_cases/42-411445/
someone stated "The step in the chamber neck is to identify fired cases as coming from a civilian rifle and not from an unregistered military rifle. This is the law in Russia."

I don't believe that's whats going on with your 300BLK brass.

I just don’t understand what benefits the stepped chamber might have?

It's das Kröpfungsliderung!

I did some interweb sleuthing and found that Georg Luger patented the chamber step in 1910. Pretty interesting, could be nazi space magic or fake science like the Blish Principle.

Here's some links to what I was able to find:
https://naaminis.com/smf/index.php?topic=6328.0

https://naaminis.com/smf/index.php?topic=6328.0   Post#5

I did some interweb sleuthing and found that Georg Luger patented the chamber step in 1910. Pretty interesting, could be nazi space magic or fake science like the Blish Principle.

Here's some links to what I was able to find:
https://naaminis.com/smf/index.php?topic=6328.0

https://naaminis.com/smf/index.php?topic=6328.0   Post#5

Yeah I found that thread as well. In a pistol the step sort of makes sense. I can even understand the Russian unregistered military weapon thing as well. But in 300 Blackout I’m really not sure what benefit a stepped chamber would have? The end of the neck is the correct diameter. So the “Step” is an expansion of the neck. The 300 Blackout uses magnum pistol powder. So much faster burning than your standard rifle powder. Or even faster than most faster rifle powders like IMR4198. I personally have not had an issue with unburned powder in my 300 Blackout. So I am not really sure what is up with the extra step? I’m probably confusing myself. 

Being that part of the neck is at .328 seems like the case neck is partially sized.

I’m wondering what happens if I resize the case? I have 3 of them to play around with. I wonder if the case is going to elongate if I resize it?

What’s the oal of the case that will tell you. Run it through a fl sizer and call it done worse case your gonna have to trim it

What’s the oal of the case that will tell you. Run it through a fl sizer and call it done worse case your gonna have to trim it

I’ll take some measurements and run it through the FL die tomorrow. I’ll report back my findings.

Took a nap this afternoon and started drinking beer after I woke up and I don’t feel like doing anything right now. 

I measured case length before and after sizing. You can see the pics below. Before sizing the case would not fit in my case gauge. After sizing it fit but I felt that the indentation where the step used to be was so deep that I felt it would separate upon the next shooting. Bottom line is it is not reloadable IMO.