Duh...The way I read Boone's affidavit it says "What appeared to be a 7.65 mauser".... THATt My Dear Johnny is NOT a description of a 7.65 Mauser.
This is most certainly a description:
"what appeared to be a 7.65mm Mauser with a telescopic sight. The rifle had what appeared to be a brownish, black stock and blue steel, metal parts."