TLock, that is a nice clean specimen of the FA 06 round that you have. This is speculation on my part, but S&W probably was considering making the FA round a commercial round, but reconsidered after the negative comments from the military. I do believe the rimmed and rimless were the same cartridge made for either revolver or auto pistol.
My take on the Auto-rim is that it was simply an expediant to make the many surplus military revolvers more user friendly for target, hunting and self defence firearms to avoid those pesky clips. . Another consideration was that it was felt that ball ammo would wear the bore faster than lead. To add to the speculation, I have seen a commercial loading of the AR with a jacketed bullet. Perhaps that one was for serious business.
I sure wish I had bought several of both brands of revolvers while they were thirty dollars or so from the surplus dealers.

Ken