Your ranged auto attacks have a 8% chance to trigger Lock and Load, causing your next two [Aimed Shot]s to cost no Focus and be instant.
Lock and Load is a passive hunter talent available at level 30 for hunters who have chosen the Marksmanship specialization. When it activates, it allows the hunter's next two [Aimed Shot]s to be fired with no cooldown (though it still invokes the global cooldown) and no focus cost.
Patch 7.0.3 (19-Jul-2016): Black Arrow and Lock and Load moved to Marksmanship-specific talents.
Patch 5.1.0 (27-Nov-2012): Lock and Load will now activate correctly when Ice Trap is triggered by an immune target, as long as a susceptible target is within the area of effect.
Patch 4.3.2 (31-Jan-2012): Lock and Load no longer benefits Arcane Shot, nor is it consumed by Arcane Shot.
/Patch 4.0.1 (12-Oct-2010): Description changed from You have a X% chance when you trap a target with Freezing Trap, Freezing Arrow or Frost Trap and a Y% chance when you deal periodic damage with your Immolation Trap, Explosive Trap or Black Arrow to cause your next 2 Arcane Shot or Explosive Shot spells to trigger no cooldown, cost no mana and consume no ammo. This effect has a 22 sec cooldown.
Patch 3.3.3 (2010-03-23): Fixed a bug where Lock and Load always proc’d 100% of the time from the first tick of Explosive Trap and never from additional ticks. It should now be 6% as advertised.
Patch 3.2.0 (04-Aug-2009): Now has a 22 second cooldown. The Lock and Load effect cannot be obtained on targets immune to snare effects when Frost Trap is used. The tooltip for this talent has been updated to indicate that it also works with Explosive Trap.
Patch 3.1.2 (2009-05-19): The tooltip has been corrected to display its actual chance to occur.
Patch 3.1.0 (14-Apr-2009): Re-designed: You now have a 33/66/100% chance when you trap a target with Freezing Trap, Freezing Arrow or Frost Trap and a 2/4/6% chance when you deal periodic damage with your Immolation Trap or Black Arrow to cause your next 2 Arcane Shot or Explosive Shot spells to trigger no cooldown, cost no mana and consume no ammo. This now has a new spell effect and sound. Prior to this, it could proc off of Serpent Sting's periodic damage, and any trap.
Patch 3.0.8 (2009-01-20): Now has a 30 second cooldown.
/Patch 3.0.2 (14-Oct-2008): Added; Lock and Load now has a chance to proc periodic damage by 2/4/6% (down from 5/10/15%.)