Last year, one guy bought a brand new 9 mil semi-auto pistol, and full reloading equipment.
He filled up 9 x 19 mm casing full of smokeless powder thinking the size of casing really is the measure to load. He was not using any other measure, nor scale.
He came to our local range, to test and fired at 25 meter target.
As a result, the slide of modern 9 mm pistol came back to his head and gun destroyed.
Hospital treatment followed. He survived. The gun did not.
Lessons learned..... well, you got it!