What the heck was this fired in? 9mm Brass

[tujungatoes]

It dont have to be a SMG to have it.

Yeah, I'm familiar with fluted rifle chambers. I was referring to the pistol caliber guns.

[xfer42]

Something without a locked breach. Blow back operated. Looks like it was blown out of the breach while expanded.Just a guess.

[Kiba]

That must have been a fairly warm load to get 9mm brass to "form" to the flutes like that... or very rough/poorly machined flutes.

My reloads from my P7M8 leave the chamber with carbon "tracks" on the brass from the flutes but there isn't any noticeable gouging or forming of the brass from the flutes. After a trip through the tumbler you can't tell the brass from the P7M8 has been through a fluted chamber.

[ireload]

HK with a fluted chamber.

+1 on that.

[ponderosa]

I am going to go out on a limb and say a gun.

+1 on this

[EBR Works]

The SVT-40 is gas piston operated and has a fluted chamber as well.

[NRAhighpowershooter]

I have reloaded 9mm an 308 HK brass numerous times.. my 308 HK Brass has been loaded as much as 15 times before I'll see neck cracks.... US military rifles are harder on brass as they twist the brass out of the chamber while the HK's pull the brass straight out....