"Does anyone know if Michael specified that his guns sell in one auction?"

I think the fact that Michael had produced a list of "keepers" implies he planned to sell about 2/3 of his collection and hold back the "keepers" to a later date. His untimely death,of course,changed that.

I, too, hope having the whole collection at once is not "too much of a good thing", but a few more days will tell us the answer to that. I suppose we can judge by the percentage of the rifles that sell below,with-in or above estimate as a determiner of whether there were too many at once.