For a person with commonsense ......They would conclude that 6" X 10" would not be a "small white card"
Jerry Organ posted a photo of the bottom of the stock of a model 91 /38 Mannlicher Carcano. The bayonet slot is clearly visible , and unless there is something drastically wrong with your eyesight you should be able to see that the so called "palm print" lift on the small white index card was lifted from that area of the WOODEN stock. It was NOT lifted from the metal barrel.
Detective Day said that he spotted a print on the SIDE of the barrel about 3 inches back from the end of the muzzle end of the wooden stock. The place that Mr organ has circled and drawn a line to....( the smaller orange circle) Is about 1/2 inch back from where the end of the wooden stock would be if the stock were on the barrel.
in the colored photo the bayonet groove is clearly visible .....The end of the bayonet groove is about 3 1/2 inches back from the end of the wooden stock. So Lt Day guessed fairly accurately when he said he found the print about three inches back from the end of the wooden stock.
The only reason that I can imagine that Day used that 3 X 5 card in fabricating the tale about finding the print on the metal barrel is because he knew that he had sent that card to the FBI and he thought that they would confirm his tale.