If clip or mag fed rifle not used, only handguns, then the person would need some serious training prior. I am not an expert. We do need experts to look at the weapon situation from the point of view of 1- need for training for each condition, (handgun and rifle), 2- amount of time firing would take, (this can be correlated as much as possible with timing of phone reports etc.).
I was in a well planned robbery where all witnesses were to be killed. 45s were used. One misfired on me.
In service I fired 45 for 'familiarization'. It is much more difficult to be 'qualified' on a 45. We need some experts here. I am not but know enough that background would be helpful.