As a former soldier (MP) and civilian cop and Bodyguard as well as a firearms/tactics instructor I can tell you that a rifle may be great in a military context but not so much in a civilian world, in fact a rifle is expressly forbidden in an active shooter role for schools. OK we can bring a rifle along but not make entries into the classrooms. I do take exception with that policy but i understand it especially when there are more friendlies then bad guys in a confined space AND when a handgun is the primary weapon making it much more familiar.

As a soldier Ive carried a L1A1, a G3, and a M16, along with a few SMGs. By far the L1A1 is the longest, and yes it can be maneuvered in a doorway/room but not nearly so easily as a handgun. Now factor in an untrained homeowner leading the way with the barrel of his rifle, likely held at the hip.

Militaries issue rifles because they expect their soldiers to fight soldiers. Civilians not so much, Untrained civilians even less. Weaker civilians unused to recoil or the weight of rifle lesser so.

Brother you might want a rifle, Id take a SMG and if I couldnt have that Id take a Glock with a RMR and a 30 rnd mag; but if I was arming somebody's grandmother who could rack the slide or was recoil shy, then it might be a 38 or even 22 SAA because they can cock it and pull the trigger.

Now Id tell her to get training but know that she wouldnt and Id tell her to call 911 and hunker down behind her locked bedroom door and wait for the PD.