Hi all. Nice Discussion.
I remember when I read these stories about O-Sensei the first time, back to back. To me they demonstrated something very interesting about the founder.
In the case of the 6 shooters I think O-Sensei had time (some days I think) to mentally prepare himself for the engagement, plan a strategy or whatever you will. It did not happen on the spot, as such he entered the situation already prepared for what was to transpire, knowing what was to come. To me, foreknowledge is a major advantage in any scenario like this. It is also possible that a person at O-Sensei's level could "sense"- for lack of a better term- the preparedness and willingness of the soldiers to shoot him (thru body language, metsuke or whatever). In swordsmanship, this resolve or spirit can mean the difference between life, mutual kill or death. It is my beliefe that in this case O-Sensei knew he could dodge these bullets, not based on the skill of the men or the quality of weapons used, but on the possibility that they did not have the "heart" or "spirit" to shoot him. Hence if their intent was lacking, their technique would be as well.
In the case of the village sniper
his mental fortitude was absolute. He would kill Ueshiba without flinching, and he had the skill to do it. On the reverse side, from the story I read on Aikidofaq.com, Shioda was the one who brought the sharpshooter to O-sensei without having told him first. Hence, he was caught mentally unprepared for such a situation with the extra problem of having a worthy opponent with the confidence and "heart" to pull it off.
Wisely I think he saw the vast difference in composure and resolve between 6 sharpshooters who think that shooting is about aiming and pulling a trigger, as against a seasoned veteran who's idea of marksmanship was to visualise where you want the bullet to be.
I am very happy that he chose to back down in the second scenario, else we may have lost a very skilled martial artist. Had he had the time to prepare for this engagement as well, I am not sure what would have been the outcome.
Just some thoughts, have no more access to the facts than anyone else, but this is what I got from the story.