The unlikely circumstances of Robin Committing Suicide using a rifle with silencer attached

In the first trial expert witnesses testified that the shot that killed Robin Bain must have been delivered from a short distance, making suicide impossible.  The science of determining how close a gun was to Robin's head when discharged is fraught with controversy and there can be no conclusive way of knowing if the gun was right against the skull or a further distance of 20 cm or more. 

Joe Karam demonstrated in court that it is possible to hold a rifle with silencer attached against your head and shoot yourself in the manner that Robin was shot.  This was an important event in the trial because it opened up to a disbelieving public, the possibility that Robin could have killed himself.  However, given that the defence also claim that Robin changed and washed his clothes it seems unusual that he didn't also take the care to remove the silencer so that he could more easily kill himself without risk of missing.  A silencer can be removed by unscrewing it using the hands, an action that takes less than a minute.  You could argue that maybe Robin wasn't aware of that.  If so, then there are more secure ways of committing suicide with a rifle and the most common is to lodge it in the mouth.  This way you are ensured of success.  By holding the rifle in the manner that Karam demonstrated in court, there is a risk that by moving the hand to pull the trigger you will also move the rifle and cause the shot to miss.  Bear in mind also that is a rifle has already misfired for the killer once, and surely he wants to be spared the ignomy of a failed suicide attempt.