WordNet (r) 3.0 (2006):

let fly
    v 1: fire as from a gun; "The soldiers let drive their bullets"
         [syn: loose off, let fly, let drive]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "let fly":
   bowl, cast, catapult, charge, chuck, chunk, cock, dart, dash,
   detonate, discharge, drop, eject, fell, fire, fire off, fling,
   flip, fork, gun, gun for, heave, hit, hurl, hurtle, jerk, lance,
   launch, let off, load, lob, pass, peg, pelt, pepper, pick off,
   pistol, pitch, pitchfork, plug, pot, potshoot, potshot, prime, put,
   put the shot, riddle, serve, shoot, shoot at, shoot down, shy,
   sling, snap, snipe, strike, take a potshot, throw, tilt, torpedo,
   toss