Bearing in mind that Ralph said that Sheila had already got the gun, and that we assume it was loaded, I find it hard to reconcile that the close quarters combat then takes place (the battle whereby Ralph gets battered and Sheila hardly gets scratched). Regardless of my view on that, however late the last phonecall to the outside world purportedly was, the timescale for the fight, the reloading, the shootings (in whatever order) become tight before the police arrive at around ten to four.