I no this is no great observation on my part and most have probably seen this before but I thought it was pretty wild. I noticed the inside wall lining of this fired 40mm case had the imprints of the powder left on them. The cool thing is when the multi-perforated powder grains were at a 90 degree angle to the side wall of the case it clearly shows the perforations. I am not 100% sure, but this looks similar to the physics of a hollow shape charge principle I saw on Future Weapons??? I forgot what they called the principle, it was named after the scientist who discovered it. I could be way wrong?