I spent 23 years in the military (1987-2010), most of it as a SF weapons sgt., to include being a instructor at the course that produces SF weapons sgts. We never did this. It sounds like an exercise that would likely result in lost/launched gun parts, and possibly broken weapons- at least the possibility of an eye injury from a launched part would be mitigated. A test that we did do when I went through training was called the "pile test", where a handgun, SMG, rifle, and MG were fully disassembled, placed in a mixed up pile, and the student was required to fully assemble 3 out of 4 to pass, with a time limit. I had a 1911, a M3 SMG, a Garand, and a M1919A6 MG (WITH headspace set)- over 100 individual parts. I believe the time was 20 minutes. I thought this test was stupid when we did it and I still think it was stupid. When I went to work there years later, it had been removed from the course.