On page 344 here, (Gunsmithing by Roy F. Dunlap - 1963) http://books.google.com/books?id=7Ab12fH...shotgun&lr= , are some published tolerance for German chambers followed by 65mm cartridge info. Previous pages have some British info regarding 65mm/2 1/2" actually being 2 9/6ths inch.

Kind Regards,

Raimey
rse