Well, I'm not one to question the credibility and veracity of those who are reporting the effect of this scratch rifling, and I don't "know", for certain like first-hand experience about it, but it seems hard to believe for me. Think about how much trouble we have getting the right patch and ball combination to perform with conventional rifling! Just how effective is a bunch of scratches, hardly a thousandth of an inch deep, going to impart rotation to a ball that will tear an .020 patch to shreds due to sheer stress if the ball is just a scoche too small? When the powder is ignited the ball has inertia - both translational inertia and rotational inertia. How are the very shallow scratches made by coarse emery grit going to provide enough engagement to accelerate rotationally a heavy lead ball? It just doesn't compute in my old brain. Something isn't right.
The dueling pistols mentioned above were rifled for the first 2/3s or so and then reamed smooth to make them appear to be smoothbores even though they had rifling. But that rifling was deep enough to engage a conventional patch. Yes it was a "cheat"! But I guess if your are willing to kill somebody you aren't worrying too much about deceiving them. Right?
Best Regards,
John Cholin