I like Lon's suggestion, Roger - it's a good one. I have difficulty with integrity using .020" patches in my .40 with a .397" ball using 3f powder, but they're just fine with a .400". Even a .017" stretchy twill works perfectly with the .400's, but not with the .397's. The .375" is round at .397"x.397" as well as the .400" being round at .400"X.400". For the .395" ball, I have to use a .0215", 12 ounce denim. I've not found a twill that is heavy enough for the smaller ball. This is with 65gr.3F. GOEX 2F allows me to use the thinner patches, with good accuracy and no cutting or burnouts.
I think to get a burnout, one needs one of three possible problems. 1/. Loose ball/patch combo. 2/. A cut patch on loading will also result in a burnout. The third is kinda scary - a crack starting in the interior of the bore. This may require a hawkeye bore light to see. Pulling the breech may be all that's necessary.