1) you are erroneously suggesting that when a shot is fired with the moderator attached it will definitely leave a ring around the wound, this is not true. It CAN happen but doesn't have to happen. It doesn't always happen.
It is POSSIBLE for a contact wound to burn an impression of the barrel of the weapon (moderator if a moderator is attached) into the skin but it doesn't always happen and didn't happen in this case. If it had happened in this case they would have tried matching up the impression to the rifle barrel itself and the moderator and evaluated which it matched. There was nothing to match because it didn't happen.
The defense argument is effectively that it wasn't actually a contact wound because no impression was burned into her skin. But since it doesn't always happen with contact wounds this argument will not go anywhere legally.
2) the blood would have been in the rifle if the moderator had not been attached. The blood was in the moderator not the rifle and was distributed exactly as it would be from drawback. This is proof it was attached when she was shot.
1. Abrasions rings are left when the barrel is in contact or very close contact to the skin hence why I mentioned the autopsy report.
2. The DNA found in silencer was more likely to be Junes this was confirmed by Webster and got Bamber his appeal hearing in 2002.
3. The alleged blood flake belonging to Shelia was found in 5th baffle plate no where else. The Bourtflours took the silencer apart with their bare hands, the same day they collected blood stained clothing and a pair of sheilas blood stained underwear from WHF.
4. The Drawback effect does not always happen. Macdonell and Brooks done original research in blood splatter drawback and found it was more likely to occur with a shorter barrel and a higher calibre weapon. The shorter the barrel the more drawback the higher the calibre the more draw back. Being a .22 long rifle the odds are minimal.
Further reading
" Principles of Bloodstain Pattern Analysis: Theory and Practice
By Stuart H. James, Paul E. Kish, T. Paulette Sutton"
5. This is the baffle plate in question

Mark Webster a forensic scientist in his own words
"
No blood was visible on or in the moderator. Limited chemical testing (KM testing) did not reveal the presence of any blood. The red stains on one of the baffles removed from the moderator shown below were not blood. They were probably rust. The flake on the rim of the baffle appeared to be "soot". Several such flakes were present inside the moderator."