I got this rounds today, but don’t know what it is. It is a brass case headstamped “* DAG * TROISDORF”. It has a very rounded copper primer cup. It is straight walled and rimmed. Measurements are:
Case length: 0.7"
Rim diameter: 0.43"
Rim thickness: 0.04"
Outer case diameter at head: 0.39"
Outer case diameter at mouth: 0.39"
Inner mouth diameter: 0.37"
This looks to be some sort of blank with fine grey powder stuck into the bottom of the case, and appears to never have had a bullet.