I have heard both stories.. and both "sides" seem to speak with equal conviction. Lucky enough for me, by using the proper size balls and the wad as I outlined, I have yet to encounter a single chain fire. Could there be other factors involved? Of course, but there is no reason NOT to try and be safe at both ends. If i ever DO have a chain fire, I'll have to look into it a little deeper.. But so far, so good.
In talking with High Master shooters they say chain fires come through the nipples, I trust them over internet experts who do not know how to clean their guns and load them.
"Actually when seating a ball on top of wads, the ball pulls the wad from away from the cylinder wall and creates a gap where the wad does not fit any more to the wall. The gap is created from the wad forming around the back"
"That makes sense... I think.. But what does it MEAN exactly, in terms of performance and safety?"
Get you a piece of clear hard plastic, push in a wad and seat a ball on top of the ball and see what happens to the wad.
Safety, the wad does nothing, performance it does nothing. I guess a wad does in a minor sense, it moves the ball closer to the forcing cone and reduces the amount of jump for the ball.
I have been mentored by some of the best B/P shooters in the country and they have been able to teach what works and what is useless.
When the ball is seated a lead ring is cut, the extra effort in seating a .454 versus a .451 come from the ball entering the chamber, no increase pressure when seating the ball unless you force the loading lever down.