What is the delay time for your camera, between pressing the button and the shutter release?
Let's say it is 0.01 sec, a hundredth of a second. (I bet it's more than that really..)
So the combro registers the pellet passing the first sensor and instantly signals the camera to fire. No software delays at all. The shutter release sequence is initialised and 0.01 sec later a picture is taken.
Where is the pellet, that the combro detected? Well, it's doing roughly 800 feet a second, that is 8 feet in a hundredth of a second. 8 feet from the muzzle.