I find it pretty hard to imagine the family going to bed as usual, if Sheila had fired a shotgun in the kitchen earlier on in the evening.
Hi shona, If a shotgun cartridge was discharged in the kitchen the night before the murders evidence of the blast would be fairly obvious.
I have asked Mike T before where the Raker cartridge, alleged to be associated with this discharge, was supposedly found, but no reply so far. I feel it was not in the kitchen for the reason stated above, but somewhere outside the house (and spent gun cartridges on a farm I'm sure are relatively common).
If a shotgun blast was heard that night I may simply have been let off outside to scare vermin. As far as I can tell there is no indication a shotgun was used in anger against persons (and Shona I am with you on a third party's involvement, with JB's knowledge, and have posted on this some months ago in a debate with Kaldin).