Can anyone recommend an accurate and physically small 1/2" drill
chuck?

My milling machine doesn't have much Z-axis space, so I hoped to
improve things by buying a set of screw machine drill bits along with
what I hoped would be a small drill chuck. But, the 1/2" Jacobs "Ball
Bearing Super Chuck" that arrived yesterday is massive, about the size
of an ordinary 3/4" chuck.

I chose this particular chuck because the literature claims "The
world's most accurate key-type chuck."

I have a salvaged 1/2" Jacobs chuck that is nice and compact and I
expected to get something of similar size. Was I ever surprised!
I'd use what I have, but it has a threaded mount and is getting
somewhat tired.

My catalogs show a conventional Jacobs and a Rohm, key type. I don't
know which one will eat up the least Z-space. If any of you know
which of the two is shorter, or, if you know of another brand of 1/2"
chuck that would fit my needs, I'd like to hear about it.

TIA

Orrin