If the killer didn't wear gloves then the killer's prints would have been in the blood that was on the rifle and that means blood would have been on the killer's hands to leave bloody prints on other objects the killer touched. Moreover, when the stock broke the killer's hand would at minimum have been scratched and more likely cut. Sheila's hands had no scratches let alone cuts and there is no proof Jeremy's hands had any wounds either.
You deliberately ignore the fact that both Ralph Bamber, and Sheila Caffell, had things of importance together, which make the struggle far more likely to have been between Ralph and Sheila, rather than between Ralph and anyone else. You over look the fact that marks upon Ralph's arm, and marks on Sheila's right wrist and right forearm, are perfectly consistent with both having been involved in some sort of a struggle together. Furthermore, both Ralph and Sheila had blood on the fingers of their hand. Additionally, sheila had blood on the soles of her feet indicating that June had already been shot before Sheila's feet got contaminated with Junes blood. Ralph had clean feet, thus enhancing the fact that he never entered the main bedroom after the shootings had started...
Bearing this in mind, the short conversation Ralph had on the phone to Jeremy, makes absolute sense, because by that stage all that Ralph knew for certain was that Sheila had got one of his guns, and that she had shot at him at least once, but possibly twice, and that she was going berserk. He didn't know at that stage that Sheila had shot June 5 times in the main bedroom, or that she had already killed her two young sons in the other bedroom. If Ralph had known this, he would not have wasted any time in phoning Jeremy, he would have called for the police, and ambulances...