Groove on the upward face of ammunition magazine, was positioned in such a way, that any blood which dripped from Sheila's hand or fingers or her wrist, could have leaked into the magazine where bullets were later loaded to carry out unofficial and official test firings of control ammunition...
Once you load a control bullet (or more) into a blood contaminated ammunition magazine, any blood which was present there, before the control bullets were loaded up into it, could be carried on the control bullets into the working mechanisms of the Bamber rifle and when discharged this could have been a source from which a small flake of blood was carried into the silencer, from where the ballistic expert later recovered it, that allowed him to introduce his theory about backspatter...
