locked and loaded

( adj.,obs.)

   [from  military  slang  for  an M-16 rifle with magazine inserted and
   prepared  for  firing]  Said  of  a  removable  disk  volume properly
   prepared for use -- that is, locked into the drive and with the heads
   loaded.  Ironically,  because  their  heads are `loaded' whenever the
   power  is  up,  this description is never used of {Winchester} drives
   (which are named after a rifle).

[glossary]