5mm sounds a bit 2 much, from memory the bolt on my dm4 was pratically flush with the rear of the breach.
Do you have an oring in position 10, if there isnt put one there, if there is one you could try adding another infront of it to make it thicker which would make bolt rest further forward.
If there is an oring there and its sitting that far back in the breach i would be inclined to think that there was an error when either the bolt or the body has been machined. If you can find another dm5 to compare it to that would be good.
anyone got a picture of the breach of there dm5? (looking down through the feedneck)