I'm no RE expert, but isn't Alice a cloned/genetically-engineered super soldier that slays thousands of Umbrella Corp. flunkies/zombie dogs/ugly zombie brutes/other super soldiers? Given that fact, is it that implausible that she can use a shotgun one-handed...
Well, there you go - I didn't know that and thought she was just a security type person but having only seen the very first film in the series a good while ago maybe I'd just forgotten she was super-human.
EDIT: Just checked the oracle and, yes, I see what you mean, and I quote "She arms herself with a shotgun and wanders around the city looking for supplies. She is constantly disturbed by a man who keeps showing up in visions, who was revealed to be experimenting on her; she now has superhuman agility and strength."
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Whatever the merits or otherwise of these films they were all big box office with this one alone making over $129M on a budget of $45M with worldwide grosses for the first five films of almost a billion dollars and holding the record as the most successful films based on videogames.
Positive reviews included:-
"It's a fun kind of stupid" The Oregonian
"When Milla finally starts kicking zombiefied ass it becomes good enough" AV Club
"Anderson's screenplay provides a steady series of inventive action situations, and the director, Alexander Witt, makes the most of them. His work is fast, funny, smart and highly satisfying in terms of visceral impact" New York Times
Most quotable "anti" quote goes to Roger Ebert with "Parents: if you encounter teenagers who say they liked this movie, do not let them date your children".
....and that super rare azn one is just parts 1-3 and too damm expensive lol 
...why zavvi gotta do random RE movies by themselves without the other parts? 
also the moment she randomly starts using Jedi force powers makes the semantics of handling a shotgun slightly irrelevant 
