Wonderful rifle, you will love it. As stated the 275 is the Rigby moniker for the 7x57mm mauser round. A really nice light rifle. Praise be with our Lord that no one installed a scope.
My only critque is if you are sure of year of manufactor as it has modern "looking" lines to the stock which is something that appeared on Rigby's after the last war. I am sure I can be wrong on this, just an observation and a wish to be enlightened.