They need to receive basic firearm training and familiarity.

Then once they have a little bit of time under their belts they can make a more enlightened decision about what their comfort level is and what kind of firearm makes the most sense without being too intimidating or impractical in the circumstances.

If they are truly comfortable with a shotgun and can demonstrate capability so be it...but my recommendation would be a revolver which they can manipulate without it being too difficult for them to operate.

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642-1, M&P15 TS