From CCI's web site:
http://www.cci-ammunition.com/ballistics/rimfire.aspx
FROM SMALLEST TO LARGEST IN SIZE AND VELOCITY:
22 Caps:
Usually light bullets like 29 grain or round ball at about 500ft/sec
CB Short/Short:
Usually light bullets like 29 grain at around 7-800ft/sec
Long:
Usually lighter bullets like 29 grain at around 1000ft/sec
Long Rifle:
Usually heavier bullets like 40 grain at around 1000ft/sec
Magnum:
Usually heavier bullets like 40 grain at around 1900ft/sec
Obviously there are High Velocity versions of most pushing velocities up a couple extra hundred feet/sec.
To answer your question dirrectly, case length and velocity.
