Hey Broken,
I have never used any press with any sort of powered cycling, so I may be missing the barn by 12 yards on this. First, the title of your thread mentions an auto drive for a 366, and I am assuming you are talking about the Pacific/Hornady 366 progressive shotshell presses. I have a Pacific 366 in 20 guage, and two Hornady 366 presses: one 16 guage and one 12 guage. Prior to my 366s, I had a few of the earlier generation Pacific progressives, and I have a deep appreciation for the evolution to the 366 presses.
In my experience with all of my progressive presses, I have never felt the operating cycle would lend itself to any automatic drive mechanism. There are just too many cycles where I "feel" something happening that requires me to hold the handle in place while I check things out to make sure things are going correctly. One for example would be the one brand of plastic wad that uses eight small petals rather than the more common wads with four petals. The four petal wads rarely get hung up in the reloading cycle, but the eight petal wads frequently have a petal get out of place, and I have to hold the handle in place while I free the offending petal. If an automatic drive system were in place, the errant wad petal would be stuffed in without any chance for me to "feel" the difference.
Like Deaf mentioned, if 500 shells at a time is too many, cut it down to two 250 shell sessions or even five 100 shell sessions. I am old and beat up with arthritis in my joints, but a 500 round session on a 366 does not bother me so far (knock on wood). If 500 rounds did bother my joints but I could do a 100 round session with no complaints, I like reloading enough to switch to doing five 100 round sessions.
I really do enjoy the time I spend reloading, and I do not look at it as a necessary evil just so I can go shooting. I hope you are able to work out your difficulties and enjoy your reloading as much as I.
Best wishes,
Dave Wile