The panel with the yellow sticky tape upon it, is the underside of the kitchen mantelpiece at whf, and the other panel with the "U" shaped mark, is the vertical panel of the aga surround...
The "U" shaped mark, on the vertical panel of the aga, was made by the barrel of the gun being thrust / pushed up against it..
The other marks on the underside of the mantelpiece, were made when the fore-site on the top of the guns barrel was brought / came into contact with it, during some kind of movement of the guns barrel in that location at one time or another...
None of these marks were made by a silencer having been brought into contact with the aga, either the vertical face, or the underside of the mantelpiece...
In my opinion...
I don't think that happened. The marks on the underneath are not aligned with the scratch on the vertical. I don't know what made those scratches but there's no reason why the same part of a gun or silencer didn't make them all.
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Well, I disagree, I think that the marks on the vertical and the corresponding marks on the horizontal are inextricably linked together, and as we now know, DS Davidson (8th August 1985 - and 1st October 1985) refers to those marks as having been made by the barrel of the gun, not the silencer...
In my view, this is sufficient to warrant taking the view that the marks on the two planes of the aga surround, were made by the guns barrel coming into contact with the mantel-shelf, not the silencer...
They probably are linked together in that they were probably made by one object at the same time - not the barrel of a gun and the foresight at the same time. There's no way to tell what made them, other than the paint found on certain objects. It could have been a silencer, a barrel of a gun, or another object.
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Well, I disagree - if the end of the guns barrel was forced or pressed up against the vertical panel of the mantelpiece, and the barrel was moved so that it went upwards until the fore-site on the guns barrel came into contact with the underside of the mantelpiece, you could get the marks that have been photographed there, on the underside of the shelf...
What would be relevant in such circumstances, in my opinion, would be the mark on the vertical panel and its characteristics and dimensions, and the gap between the corner of the aga (vertical /horizontal angle) on the underside of the mantelpiece to where the marks commence. This gap is or could be the same as the distance between the end of the guns barrel, and the position on the barrel where the front part of the fore-site is situated...
I think it is ore than a coincidence that the horseshoe mark on the vertical panel is very similar or identical to the dimensions of the guns barrel (end), and that the gap from the corner to the position of the marks on the underside of the mantelpiece are similar if not identical to the gap, between the end of the guns barrel and the commencement of the fore-site on that guns barrel, for it not to have been the guns barrel which made those marks...
If the silencer made these marks, the characteristics and dimension of the "U" shaped mark on the vertical panel would be considerably different, and there might not be / would not be the gap from the corner to the commencement of the marks on the underside panel...
What seems to be important to me, is the presence of the yellow sticky tape on the underside of the mantelpiece in the attached photograph...