bilesteve
I'd say it depends on your rifle. Using modern smokeless powder usually never hurts, its the primers that can cause issues on short term.
Long term storage might cause problems, but if your gun shoots more consistant dirty, then after a long range day, clean it then fire enough rounds that put the Point Of Impact where you left it and put the gun away.
That's how I use mine and so far no problems.
By the way, all my rifles shoot different from a clean bore than a dirty one, not just NEF's