The difference that you note is the difference between hand times and fully automated times. High schools usually use hand times which are generally .21-.23 seconds faster than the times at the nfl combine where the official times listed are fully automated times. This difference is generally human error as the person timing usually starts timing by reacting to the runners first movement and thus slow on the start. The person timing is usually standing at the finish line and generally stop the time when the player reaches them rather when the player is passed them in turn stopping the time too quickly at the finish.
So to relate this back to the topic, my guess would be that if Kilgore ran a 40 monitored by a fully automated timing system it would be in the 4.7 range.
