First, I provided evidence for my claim.
No you didn't. Speculation is not evidence.
Second, Martin's current positions is this: Hill made off with the revolver by himself for some period of time before it was turned into the Homicide squad. He hasn't provided any evidence for this happening,
Strawman. Martin never claimed anything of the kind.
Third, Carroll is the first Police Officer that can be shown to had uncontested possession of the pistol. This is not true for McDonald. So he is the first to have unambiguous custody of it.
Made-up BS. All of these "possessions" are contested as undemonstrable.
As for your statement that Carroll "didn’t even know whose hand he grabbed it from," we don't just have Carroll's word for it. Carroll said that he grabbed it after he saw someone hold it towards him from out of the scrum. McDonald said he held it out of the scrum and "gave" it to Carroll.
And did he "know" this before talking to Carroll later? Unknown and unknowable.
Carroll said he received only one gun from the scrum. McDonald also did not mention giving a second gun to any one. No one reported a second gun or two guns being involved in the scuffle. The logical upshot is Carroll got the gun from McDonald, whether or not Carroll recognized who he seized it from. Carroll giving the gun to Hill doesn't change this. It just adds Hill to the chain of custody. And it especially doesn't matter if Carrol remains with Hill.
This is all blather to try to excuse away a lack of a chain of custody. It still remains that McDonald was the only one who could establish that a gun was ever in the possession of Oswald, and he had no basis for identifying the gun Hill pulled out of his pocket hours later as the same gun. Apparently the cops were more interested in playing a game of "hot potato" than they were in the provenance of evidence.