Danish 30-06 case

Anybody any ideas regarding this fired danish 30-06 case, shown next to a standard Danish M60 Blank.
Headstamp is: AMA 58
2nd step of the case is thinner than the top part of the blank. Inside case mouth is aprox. 5,25 MM


Is that a crack in the extractor groove?
Have never seen anything like this before. Any residue inside?

no, that’s not a crack. There was some white dust / chalk or whatever.
While wiping it away, I noted that the rim is thinner than that of the blank.
But that is hardly visible on the picture. It is about 0,94 MM versus 1,22MM of the Blank.
The inside is clean.

It does look like a crack or something.


The long blanks were made specifically for machine gun use, M/51, M1919 etc, but this one looks like it was used as a grenade blank if it is fired, maybe for line launching. Personally i’m leaning towards a reject that has been sold and used privately or commercially.