As I often say Surp - and they tell them on day one of the sniper courses, the difference between snipers and hunters and target shooters is that snipers are the only ones where the quarry are/is liable to shoot back. That's the reason why target rifles and hunting rifles never (?) make it past the first hurdle during sniper trials.

I think I can say without fear of contradiction that the only time we have allowed a bit of user control over the rifle is with butt length and the shape of the cheek piece/rest. Just recently we have allowed a bit of autonomy with the trigger adjustment. But even then, the Armourers ALWAYS have the last say