This is one of the reasons why I think there were possibly three different weapons used, maybe as many as four in total, in these shootings!
Having said that / this...
I think that one of these weapons, that although the gun did get discharged, it damaged a ceiling light situated in the ceiling of the kitchen. It wasn't until after the 8th August 1985, that SOCO discovered that a shotgun had been discharged recently inside the kitchen. Cops used a metal detector and found all the pellets which had been discharged from a spent Raker Cartridge case found in the breech of a 12 bore shotgun in the downstairs office. When this shotgun was eventually fingerprinted the fingerprints of Sheila Caffell and Neville Bamber were found upon strategic parts of the shotguns barrel suggestive that there may have been a struggle involving both of them over control or the possession of the shotgun (either after a shot had been discharged from it, or just beforehand). In point of fact, the guns barrell which DS Davidson spoke to COLP about in his 1992 police interviews, where he talks about Cook handing him a paint sample (RC/1) at the scene on the 8th August 1985, was because some paint had been found on the end of a guns barrel, a gun which had been found downstairs at the farmhouse on that same date ( the 12 bore shotgun)!