It would be impossible for both of them to be the last one in the clip.
No, it's not impossible....It seems impossible to you because you believe that those shells were fired that day. What the abrasions tell us that both shells were the bottom shell when they were fired on the rifle range, and then picked up and possibly used as filler in a clip for practice with the rifle.....so they could have been the bottom shell in a practice clip.
The only thing is - the conspirators (who had intelligently and meticulously planned everything in order to frame Ozwald) would HARDLY have left an unfired rifle in the TSBD. A sniff test would instantly prove that the gun hadn't been fired. They couldn't have known that there would be no sniff test.
So, there are many possibilities:
1. The rifle had been fired - but the guys forgot to do a sniff test (unlikely)
2. The gun hadn't been fired - but the guys forgot to do a sniff test (unlikely)
3. There
was a sniff test which detected gunpowder odor but the guys higher up later needed to give the world a lone assassin and it was scratched off the record.
4. Certain officials of the DPD were part of the conspiracy from the outset (which I doubt very much). They faked or didn't do a sniff test.