I have a Ruger 77R that is marked "7MM EXP REM", SN 771-440xx. I called Ruger and they said that they never stamped the 280 barrel with anything but "280 REM", but this is clearly a factory barrel.
John Lacy's book on the Remington 700 family of rifles has a section on the odd factory markings, including the 6MM REM MAGs with the "MAG" x'd out and the 280s that were marked 7MM REM EXP or 7MM-06.
JEff
