Have you slugged your bore so you can tell the judge the measurements across both the lands and grooves? I bet the bore across the lands is .40", but the measurement across the grooves is going to necessarily be larger. When you seat the ball, it "may" expand slightly when you seat it since you are seating it with some force to make sure there is no airspace, which could pose a safety issue for you and fellow hunters in your shrapnel range. I know, I know, work with me here. We're trying to get you the benefit of the doubt. So your slightly expanded ball (due to the seating) is sitting on top of your powder, and you fire it. The kick in the pants from the high pressures of being fired further expands the ball to your groove diameter, (I mean, how strong can a piece of cloth be, right?) which is over .40", making your gun and load combination perfectly legal. If the judge doesn't believe you, bring a ball or 3 to show him that they are round, then drop them from shoulder height on a hard surface, show him the flat spot, and have him tell you that it will not expand from 20-30K lbs worth of pressure hitting it upon firing. I mean, how can the judge argue with physics when you show him the proof right there in his own court room?
And yes, I know that those of us that use these things know better and would probably have a hard time keeping a straight face with this, but, dang it, you acted in the belief that you were following the law, and your "bullet" expands to well over what the law requires, and in fact, starts expanding before it even leaves the gun. If that ain't following the law, I don't know what is.
Hey, it's worth a shot.