By the way, try reading the 1st paragraph from this interview with Koichi Tohei Sensei.
Also Kenji Tomiki Sensei avoided the question in a very diplomatic way
I must add that the stories that I read myself seem to be like duels when someone was deliberately shooting at Osensei. In this case, I doubt it that opponents really shot to kill, as this would be a crime, and then this would be against Samurai ethics to shoot an unarmed man in a duel. Probably the opponents did not aim very accurately.
The fact that Osensei was constantly moving probably made their task even more difficult.
Put in this way, there would be nothing super-natural about Osensei except his courage and his bravery.
Fortunately, Osensei was never hit, because then Aikido would have never been created.