55 grain bullets tend to do some wicked tumbling once they strike skin and bone. They also will not got completely through your sheet rock wall.
Just plain ol' 1/2" or 5/8" sheet rock isn't much of a barrier. Every 55gr round I am aware of will sail clean through multiple layers of sheet rock if you miss the target.
And not all 55gr ammo is the same, not all 55gr bullets tumble, and not all of those that do tumble will break apart - and if they don't break apart into tiny fragments they will penetrate more. Even with rounds that do commonly tumble and fragment like M193, the phenomenon still isn't 100% reliable.
I just want people to understand that just because you are using an AR and some highspeed ammo, you don't get a free pass to ignore your background.