I never understood the purpose of those posings with the rifle. Yes, they prove that Sheila could have shot herself with the sound moderator on; but hey, she couldn´t have shot herself, died, then gotten up, wrapped the silencer up and put it in the cupboard, then stumbled back to where she shot herself.
Bet you´ve heard that before. 
She didn't, the silencer was not fitted to the guns barrel that fired the fatal shot under the chin - therefore, there was no need for her, or any would be killer to remove the silencer from the guns barrel after they killed her, and for them to take it downstairs to hide it in the gun cupboard, in the downstairs office. It is completely absurd to suggest that Sheila could have done this if as you say she was already dead, and it would be even more absurd for any would be killer to shoot Sheila under the chin with a silencer fitted to the guns barrel, and then to remove it after he had shot her, and conceal it as desccribed - there would be no need to use a silencer when any would be killer was shooting Sheila under the chin, and then remove it after he shot her, he would simply have shot her by use of the gun minus a silencer, surely?
In any event, the killer, or Sheila, made such a good job of using the silencer to help them end Sheila's life, that DS "Stan" Jones, came along that very same day and took possession of a silencer (SBJ/1), so if the silencer was used by either Sheila, or Jeremy, or as the case may be, by any as yet unidentified killer, and DS Jones seized it, and retained it, along with three other exhibits that he took possession of at the scene on the first day of the police invesdtigation...
They didn't do a very good job of hiding or concealing it, because DS Jones found it along with three other exhibits on that first day of the police investigation. Lets get the facts right, DS Jones took possession of that silencer, as part of a batch of four exhibits that day, bearing the identifying marks of SBJ/1, SBJ/2, SBJ/3 and SBJ/4. Lets go a bit further, for arguments sake, and say that one of these four exhibits was a photoghraph which DS Jones took of the downstairs toilet, and another was a photograph taken by him that morning (7th August 1985) in the kitchen. Now forgive me for being persistant, but I thought PC Bird was the only police officer who took crime scene photographs inside the farmhouse, on that first day? This is getting very interesting, since it appears that PC Bird and DS Jones were now taking pictures at the scene, on the mroning of 7th August 1985...
Now if PC Bird was taking photographs as part of the CID investigation into the incident, who the hell was DS Jones taking photographs for, since officially there is no records that DS Jones took any photographs at the scene that morning at all, other than references to entries in a police property register - so, did DS Jones take photographs and seize a silencer (SBJ/1) from the scene, as part of the Special Branch investigation, into the matter?
How can four exhibits (One of them a silencer) bearing the identifying marks of SBJ/1, SBJ/2, SBJ/3 and SBJ/4, disappear of the evidence radar...