The problem with this ingenious if implausible theory is that going off Jeremy's version of events it was Nevill himself who during the course of the brief telephone call laid the blame on Sheila's shoulders.
Maybe, by that stage (his call to Jeremy at about 3.25am, followed by Neville's call to police at 3.26am) Neville had only been aware that Sheila had got one of the guns? It's possible, that Neville Bamber wasn't forced by either Sheila, or her accomplice to make the call to Jeremy, or the call to the police, since both calls were made one straight after the other, Neville Bamber to Jeremy, then Neville Bamber to the police (3.26am)! This is borne out by the reference when Neville spoke to Jeremy, he said, 'Sheila has got the gun', but he told the police something slightly different moments later, when Neville said, 'my daughter has got hold of one of my guns'..
To Jeremy - 'the gun'..
To the police - One of my guns'..
We know, for example, that at least two different guns were used to shoot dead Sheila, and there seems to be support for saying that not all the other 24 bullets that were fired during the tragedy, were all fired via the anshuzt rifle - everything is pointing to these killings having been carried out by use of at least two different guns, and two silencers, as well as different types of .22 ammunition!