[Wild Bill Bucks]

Almost every rifle I own doesn't like a clean barrel. I always shoot a couple of primers off, with no load in the barrel, before loading. This fouls the barrel so that my first shot is as accurate as any other. If you are going to clean out between every shot, and the first shot is consistently in the same spot, then you can sight in with that shot. In the field it is difficult to always clean between shots if you need to get re-loaded quickly, so I would foul the barrel and then sight in with the rifle that way. This procedure is for muzzle-loaders.
If you are sighting in a high powered rifle, then simply sight to the group, and don't clean your rifle before the season is over.