You may wan to buy an L, first.
Seriously, for self protection you can’t do better than an AR-15. Very light and easy to handle, easy to use and maintain, easy to aim and very lethal.
Hunting rifles might be better at 100+ yards but for self defense, you’re interested in targets within 25 yards. You want a large magazine and a rapid rate of fire. Volume is quality. If you miss with the first shot, the sounds of the second, third, fourth, etc will deter all but the most fool hardy.
Exactly my thoughts as well - at ranges in a house, you need to be as accurate with a shotty as you do a rifle; the shot doesn't start spreading for 10-15 yards, minimum.
Lots of ammo - I've never heard anyone in a firefight complain of too many rounds available! Because if at first you don't succeed,
try,
try,
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try,
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try,
try,
try,
try,
try again!