From a stripped clean barrel, within the first 2-10 shots, sometimes you will see goofy shots related to velocity. More rarely you'll see in the first 1-3 shots after cleaning some accuracy fliers. Suppressors can also cause 1st shots in a string to have low velocity (20-50fps slow). Not sure the physics behind that but I've seen it enough times with various combinations to keep an eye open for it.
Beyond that, I have not really noticed SD's to change unless you change bullet type, powder lot or type, or sometimes primer type (some cartridges are more or less sensitive to this). If you shoot 20-30 shot strings and get the SD on that, it stays within about 1fps pretty much every time until the fouling builds up to the point of significantly increasing peak pressure, at which point SD's and precision both suffer.
