They we’re all close contact shots, Nevill obviously doesn’t think he can disarm the shooter so what are his options. Does he try and get help, does he try and arm himself or does he just take more shots? It must have been quite scary for him and painful after four shots fired at him, I would say a natural reaction at this stage is, either to disarm your opponent or run, disarming the shooter didn’t seem like an option to him?
Nevill trying to disarm Bamber upstairs was not a good option.
Bamber may have more bullets he can fire as Nevill approaches. Nevill was also now badly injured so likely to lose a struggle.
Nevill had no choice but to fight Bamber in the kitchen. As Bamber had caught up with him.
Besides which it is a natural reaction to retreat.