DID DAVID KILL GOLIATH WITH A SLINGSHOT, OR A SWORD?

I Samuel 17:50  So David prevailed over the Philistine with a sling and with a stone, and smote the Philistine, and slew him; but there was no sword in the hand of David. (KJV) I Samuel 17:51  Therefore David ran, and stood upon the Philistine, and took his sword, and drew it out of the sheath thereof, and slew him, and cut off his head therewith. And when the Philistines saw their champion was dead, they fled. (KJV)

Note that these passages are consecutive, which makes a true contradiction unlikely.  To 'slay' can mean to deliver a fatal blow.  In verse 50, David delivered a fatal blow to Goliath with a slingshot.  Goliath was dying, but not dead.  In verse 51, David took his sword and cut off Goliath's head, thus putting him out of his misery.  Not a contradiction.