As I stated in the past, this is one of those questions that will go unanswered unless Jeremy decides to stop with the lies and provide a complete run down of the murders. That would entail him remembering what actually happened, it appear she has hidden such from his mind, having the desire to be honest, because in addition to being wrong by purging it from his memory he still could lie instead of being fully honest if he did confess, and thus revelaing everything.
I don't have any expectation for this to happen ever.
There is simply no way to know whether Nevill chased him and he fled to try to reload in peace or whether he chased Nevill to prvent Nevill from reaching a weapon, phone or even exiting the house to go look for help.
There is not enough evidence to demonstrate for sure which is the case and I choose not to speculate. The question only matters to the curious human mind it has litle difference on the important facts of the case.
In either case the result was the struggle over the weapon in the kitchen, Nevill being beated unconscious, the killer reloading and firing 4 rounds into his head killing him.