I've looked again at the diagram of NB's injuries and the pathologist report in posts #78 and #80 along with the layout of WHF. The pathologist states wounds 5 and 6 were fired at an angle of 20 degrees downward from the horizontal position. According to the layout of WHF:
http://miscarriageofjustice.co/index.php?topic=633.msg25947#msg25947
2 steps precede the main bedroom so if the perp was standing just outside the main bedroom door and NB just below the 2 steps this could account for the angle of the shot? Two casings were found just outside the bedroom door.
I've yet to figure out the casings. Only 2 were found just outside the bedroom door. Does the deflector plate definitely push them along a path? I doubt there's much potential for ricochet for H&S ie if the force was substantial and the path unclear it could present a danger?
Only 3 casings were found in the kitchen although it is thought NB sustained wounds 1 -4 incl there. I believe an additional casing was found in the bedroom? Or was it the stairs?
As you say, it's possible that Nevill could have been shot in the shoulder and elbow as he was forced or tried to escape downstairs, although the same might have happened after being shot in the jaw and mouth when getting out of bed. His first reaction must have been to put his hand(s) up to the mouth in shock and to stem the blood flow. Once up, he might then have tried to avoid further shots by turning away to his right, stumbling to the floor perhaps on his knees when he received shots 7 and 8 to shoulder and elbow from behind. Hence the downward trajectory of the two bullets.
If the perp was standing outside the bedroom door firing shots 7 and 8 at Nevill below on the first couple of steps or lower landing, the shells are more likely to have ended up further down on the main flight and could even have tumbled into the main hall, instead of remaining on the landing area.
Those two shells found outside the bedroom were attributed to June, perhaps the final shots to her head. Why?... maybe there was a way of matching those casings to bullets recovered at autopsy. Or perhaps the firearms expert recreated the scene by imagining where the shells would land if the shots were delivered as she was lying on the floor.
According to the police and also mentioned by CAL, the missing fourth casing could have been carried upstairs because it was "stovepipe" jammed in the ejector mechanism, and was only freed by Bamber when he reached the upper landing. So it might have been one of those found there.