Do you think the smashed ceiling lightshade was while they wrestled for the rifle or while Nevill was receiving his blows?
Possibly wrestling.
The brutal attack may not have been needed as much as it did. Pure blooded anger. Jeremy inflicting the overkill in pure blind rage.
Remember taking the monetary aspect of the motive out of the equation its alleged Jeremy had a lot of anger to his family. Nevill was not just dad, he was his boss and employer. He had to do what Nevill said in everyday life. He was also closest to him out of all family members.
I believe he privately regretted the overkill down the line. It's an aspect of the case that scuppered the " shelia did it "