Sorta near the head, centerline of the neck will drop them with any expanding .223. Bullet weight will only matter depending on range.
Inside of 50yds any .223 hunting ammo will lock them up. I've used fmj in a trap in a pinch, with the same result...just extra blood. Not recommending fmj, it was something that had to be done in a hurry and only fmj available. Since then, I've always kept hunting ammo in my truck.
The neck/behind the ear shots are larger target than the heart IMO. The heart shot must be really low on the chest just a hair behind the leg.