The consensus that I have come to is that B&S tapers,
being (about) 1/2" per foot, as self holding to a large
degree, with side forces of milling cutters.
Morse tapers, being (about) 5/8" per foot taper,
will not take much side force before they unseat.
Now this is rue-of-thumb wisdom here. There is a
practical limit to everything.
I recently acquired a Pratt Whitney 2A and I found
some P&W collets on ebay. Some of the collets are
adapters, down to #9 B&S taper and #5 B&S taper.
I wondered if they were actually going to be useful
to me. Then, when talking to a friend, be mentioned
that he has a set of B&S taper end mills that we could
barter and trade on. I think they are really meant to
be used as end-cutting reamers, used more to radially
locate a hole than ream per se. Because jig boreres are
all about location.
Another interesting area that I have (personally) found
a B&S taper used; I bought a couple of ID grinding spindles
that came from a Cincinnati #2 cutter grinder. I only have
one mandrel to mount a stone, and I believe the internal
taper of these grinding spindles is #6 B&S taper, held with
a 5/16-18 drawstud. Will be making more mandrels, and
pending a more accurate measurement, I can then say for sure.
--Doozer