There does not need to be any proof any concealment of blood in the barrel because lack of blood in the barrel does not disprove suicide and likewise does not disprove contact wounds.
In Vincent J.M. DiMaios book Gunshot Wounds: Practical Aspects of Firearms, Ballistics, and Forensic Techniques, Third Edition (Practical Aspects of Criminal & Forensic Investigations)

Once again you demonstrate tremendous ignorance of the evidence in this case even though I expressly spoon fed you countless times on blue.
The expert testimony in this case was that the fatal wound was a contact wound from with drawback would occur and therefore blood would have been found in the muzzle of weapon itself had the gun been used sans moderator or in the moderator if used with the moderator. The initial shot caused her neck to fill with blood and under such conditions drawback would be sure to occur EVEN more surely if the moderator were not attached because the full effect of the gases would then be in effect.
The only way to establish it would not occur would be if one could prove it wasn't a contact wound but it is agreed by the defense experts that it was a contact wound.
The COA addressed this very issue in 2002:
"As to the moderator, there was the remarkable proposition raised by the defence case that Sheila Caffell having killed her family found that she could not shoot herself with the moderator on and instead of simply taking the moderator off and putting it down, went downstairs to an office, put the moderator in its proper place in the gun cupboard and then returned to her parents' bedroom where she sat or lay down on the floor and shot herself.
There was in addition not merely the presence of the blood flake in the moderator but the absence of any blood in the barrel of the gun, the end of which would have been in contact with her neck when the shot was fired."
The COA explained previously why this was significant:
"Mr Fletcher, the firearms expert, gave evidence to explain how blood got into the moderator if it was attached, or into the barrel if there was no moderator attached. He said that the mechanism was complicated and not then fully appreciated. However, the expanding gas when the bullet left the muzzle was under normal circumstances distributed into the atmosphere. However with a contact shot there was no opportunity for this escape and the gas would follow the bullet into the wound as it expanded. Back pressure would then build up forcing the gas back out of the wound taking with it blood and tissue which would in effect be blasted back into the barrel if there was no moderator or into the moderator if one was attached. He said that even without direct contact, the same effect might occur but only if the gap between the end of the barrel, or the moderator if attached, and the skin was less than one millimetre. He said that the likelihood of such an occurrence was to an extent dependent on the part of the body to which the shot was delivered and the amount of blood present at that point.
If the shot to Shelia Caffell, which was a contact shot to the throat, had been fired without the moderator in place, he would have expected to find blood in the barrel of the gun. If the moderator was attached it was "virtually certain" that Sheila Caffell's blood would get into the moderator. There was, he said "a very slight possibility of it not happening, but very slight".
The moderator reduces the chance of drawback very slightly but even with the moderator the chance of drawback not occurring was extremely slight.
The amount of blood inside her neck was considerable she hemorrhaged and thus drawback would occur if the fatal shot was a contact. Vanezis noting the hemmoraging inside her neck from the first shot:

The significance of that for backspatter/drawback:



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The Court of Appeals goes by the existing record int he case and the existing record is the testimony that drawback would have gotten in the rifle if the moderator was not attached.
If people want to hide from reality be my guest but as a lawyer one's job is to face reality and try to deal with it. The reality is one has to deal with not only the blood in the moderator but the absence of blood in the rifle because that is the way the courts view it.
The legal minded are concerned with what the court will require.
In any event there will never be any evidence found of police planting blood in the moderator. All places to look for evidence of such turned up nothing. Those who think Jeremy used the gun without the moderator attached are living in fantasyland he wanted his shots to be as quiet as possible in hopes of not waking anyone up and after he killed Sheila he realized the gun was too long for her to kill herself with it attached so hid it and made up the lies that the gun didn't fit in the closet with the moderator attached, got it out to go after rabbits and left the gun out without the moderator attached.
Even Jeremy's supporters know they will never find any evidence but rather than admit they were wrong they choose to delude themselves with the fantasy that there is evidence that has never been released to the defense which establishes evidence was planted. They are the same delusional people who say police failed to release all of Julie's statements to the defense and in order to support this lie they make up that there was a statement recorded every single occasion she had any interaction with police even though that is totally bogus.
Jeremy has as much chance of getting out of jail (by a method other than dying) as Obama does of being elected to a third term...