Could have missed something but...?

I'm pretty sure after the travelling folk take ALL their bullets the night before, Liam Neesons character has been saving 1 special bullet. He then catches up with Pierce who doesn't know he only has one bullet which Neeson then uses on his own man whether it was a genuine attempt to shoot thru him and take out both or not(you see Pierce actually check himself for a wound)my point is Liam at least knows he's spent his last bullet obviously he keeps up the charade of having a fully loaded pistol but after he's got Pierce to throw his knife down he still advances with the gun and raises it to shoot him as if he himself has forgotten he has no bullets!? He should have tossed the gun after he's been successful in relieving Pierce of his Bowie Knife and used that on him instead because one more time for good measure - 'He has no bullets!'
Does his character just forget this or did the writer and all the cast and crew?
or more likley did I miss something?