This is just my own opinion, but please do not alter an original rifle in fine condition just to be able to achieve accuracy with modern smokeless powders..which these rifles were not engineered around to fire in the first place.  I am not talking safety, as there are many safe smokeless loads that can be used in them.  The problem is not understanding what the designers in the black powder era were trying to accomplish.  Winchester wanted to sell repeating wouldn't do to have customer complaints coming in of rifles so fouled that repeat shots were a they designed them to fire a nearly pure lead bullet some .004-.005" under groove dia. and depend upon the hammer like kick of the black powder charge to obturate them to groove dia..and alllow repeat shots with a fouled bore.  The solution using smokeless has been addresed above.  I have thinned necks in my Winchester High-Wall .38-55 to allow seating a .380" dia. bullet for it's .379 bore.  I admit it's a pain, but I believe the pain will be less than when my widow is selling it and the buyer points out it's  now de-valued since the chamber has been altered.