Stamp marks inside of unfired brass?

[R_A_W]

What are these stamp marks caused by or what is their purpose?

There are indentations found inside each case where the wall meets the base. There are two evenly spaced side-by-side "lines", with each "line" being ~2mm tall and ~2mm apart. There are three pairs in each case, uniformly located @ 0/90/180 degrees. See the first pic attached.

Case overall length is very uniform @ 2.007" <+/- 0.0005" ***
Shoulder length is fairly uniform @ 1.625" +/- 0.001"
I didn't weight them because they shipped primed, but I'm happy to deprime a few to weigh & cut one in half for a better look if anyone is curious enough.

*** pretty sure that caliper's accuracy is one thou

 

[FredHammer]

I SWAG that they are reinforcing the web of the case. Limit case head separation.

 

[supercorndogs]

I would guess the tip of the piece that is used to support that area when they extrude the brass looks like that.

Or the tip of the piece that supports that section when they punch the primer looks like that.

 

[R_A_W]

I would guess the tip of the piece that is used to support that area when they extrude the brass looks like that.

Or the tip of the piece that supports that section when they punch the primer looks like that.

The first was my guess - that they were stamped in during cupping or the draw. But now that I think about it, the lines would be more stretched up the case walls during the draws, so they must be pressed in after final draw. My best guess now is that they're used as a mechanical lock during head turning, prior to tapering the shoulders.

These were advertised as Norma mfg'ed, but I... have my doubts

 

[Haney]

From the web.

This .308 Win brass is made by Norma in Sweden and primed by Norma using large rifle primers made by Norma in Germany. This brass is marked MAI on the headstamp instead of Norma, but it's Norma quality brass at a better than Norma headstamp price. Brass is bulk packaged.

Maybe a process in this video will give a hint ? At about the 5 minute mark shows some up close stuff...goes by fast though .

 

[R_A_W]

At about the 5 minute mark shows some up close stuff...goes by fast though .

Right around the 3:30 mark is where I figure the indentations would likely be made - either creating the primer pocket or squaring up the case head, but prior to punching the flash hole. Things are moving too quickly to get a good view inside the brass, but that's a good video.

A different video suggests the marks are not made when the primer pocket is created @ 2:30 (you can see the mandrel is smooth), but could be pressed when the case head is squared up @ 2:40


Norma's process is a little different than Starline's:

 

[R_A_W]

I guess I'll go ahead and bump this one more time to add some info for others using this brass.

1) The brass is really soft, which would suggest it actually could be Norma brass.​

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2) They're likely rejects due to physical damage to about 10% of cases - see attached photo of case necks.​

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3) This brass ships primed (unknown manufacturer), but they're pretty dirty and ignition seems to be inconsistent - I could only get 1" to 1.5" groups with them, so I'm just depriming them when I resize the necks & repriming with BR-2's. Groups shrank to half-MOA with BR-2's in unfired brass & a minor charge weight tweak to account for slightly larger case capacity (v. Remington Peters & Federal). Probably great for those fire-forming a .375 Raptor, or similar. Pics of the unknown primers & primer pockets from said primers.​

 

[R_A_W]

I'll go ahead and add a second comment to edit in the future & not bump again.

Brass weights are pretty consistent, averaging 2gr lighter than Lapua (unfired/untrimmed) & 5gr lighter than the Remington Peters (6 firings, trimmed once).

In a couple of weeks, I'll add case volumes and a pic of the brass cut in half to show the stamp marks.

Update 7/2/23
I sized 200 pieces with a Lee Collet die & RCBS dry neck lube to get 0.0015" neck tension. I've used 100 (50 of these fired once & another 50 fired twice). Holding 0.5-0.6 MOA 5 shot groups out of a gun capable of 0.4 MOA. I'm wondering if I need more neck tension.

I cut 2 unfired pieces in half to show the stamp marks (see photo). I deprimed & sized the neck using an expander ball without any kind of neck lube. The ball expander completely scratched the inside of the necks. The brass is very soft, suggesting it is Norma.

Also, I’m interested i what the two lines are (green arrows)

 

[supercorndogs]

I would just ran an expander through the brass with dinged necks, then chamfer and deburr.

 

[R_A_W]

That's what I've been doing