The Collaborative International Dictionary of English v.0.48:

Burrel shot \Bur"rel shot`\ [Either from annoying the enemy like
   a burrel fly, or, less probably, fr. F. bourreler to sting,
   torture.] (Gun.)
   A mixture of shot, nails, stones, pieces of old iron, etc.,
   fired from a cannon at short range, in an emergency. [R.]
   [1913 Webster]