I misspoke (mis-quoted) the Manual. It says: "Hornaday [sic] light magnum ammunition should not be used in a semi-automatic rifle such as the BAR. It may damage the firearm." (The msspelling came from the Manual.)
I wrote "high pressure" when I should've said "light magnum".
I downloaded the Manual from the Browning website; no telling when it was written. I didn't get it with the rifle when I bought it.