If they weren't good marksmen, it wouldn't matter what caliber they held because the odds say that they probably wouldn't hit the target anyway.
But I still think you'd opt for your loved one to have the bigger gun in the situation I described, as long as they were capable of handling it and were accustomed to at least firing it.
What do you think of this:
MEU SOC .45 continues to provide stopping power for 31st MEU.