There has been some absolutely absurd nonsensical conspiracy theories but this has gotta be in the top ten!
Swapping out the rifle from the time it was found till it was taken from the building then swapped back when it was shown to the Press later that day goes nowhere and makes zero sense.
Anyway let's summarize.
Lt. Day confirms that he retained possession of Oswald's rifle from the moment it was found till he got back to Police headquarters.
Mr. DAY. Yes, sir; this is the record I made of the gun when I took it back office. Now, the gun did not leave my possession.
Mr. BELIN. From the time it was found at the School Book Depository Building?
Mr. DAY. Yes, sir; I took the gun myself and retained possession, took it to the office where I dictated----Lt. Day first to hold C2766.

Lt. Day carrying C2766 from the Depository.

The rifle being carried from the building is definitely the same make and model as Oswald's Carcano(C2766).

C2766 being displayed by Lt. Day to the Press at the DPD.

The evidence in the OP showing the many similarities in random scratches, scrapes and gouges on the rifle Lt. Day takes from the Depository and the rifle in evidence.

Josephs extremely dishonest graphical enhancement of the "CAL 6.5" decal on the rifle to enhance a barely legible "CAL 6.5" on the rifle in evidence.

BTW notice that Griffith keeps running from my question of WHY?, why on Earth would Day or anyone else for that matter feel the need to substitute a rifle that was photographed and filmed in situ on the 6th floor, with another rifle of the exact same make and model and then resubstitute it for the same rifle originally found on the 6th floor?
Where does this go?
How does this "deception" tie into the conspiracy?
Well Griffith, waiting......??
JohnM