Well, just consider it...
The Specials are shorter than Magnums. Firing Magnums, you won't have a ring of powder in any area that the Special casing will hit. The casing of the Magnums passes that point.
If you fire Specials first, the rings will be within the reach of the Magnum casing. I forget the difference, but I want to say the Magnum casing reaches an extra 3 or 4mm past the Special's case. That is where it will start to stick.
Now, that isn't saying that a new shooter would want to go that route (Magnums, then Specials). I'm sure some would want to start lower, and work up. Either way, cleaning the cylinder will solve the issue.