Briman, you CAN use bullets intended for the .303 British and the 7.65mm Argentine Mauser to load the 7.62X54R. In addition, I have had some good results with Sierra 200 grain .308 bullets in both the .303 British and the Argentine Mauser, so would not be too surprised if the same bullets would work OK in a 7.62X54R as well. It would be worth a try. (Actually, there are some reasonably good .311" hunting bullets available in 150, 174, and 180 grains from Sierra, Speer, and Hornady.)

Keep yore powder dry!!