I agree with Clyde +1 on that. It would be interesting to know if the front of the cylinders were capped of with bore butter/Crisco or some other non combustible packing. If they were, then you could make a case for a chain fire starting from the back end. That possibility seems unlikely from my experience but I am old enough to never say never. Any more info Tac?
All I can add is I had a four shot chain fire once. After careful disassembly due to damage, those four caps were all spent.
One shot sideswiped the wedge knocking it back and the fourth went right up the rammer. Knocked the front end forward bending the wedge and peening the arbor. Found lead on the wedge and a flattened ball in the rammer which had the whole works bound solid.
That's when I replaced the original and somewhat overly used flattened I-tie nipples with Ampco's. Along with fitting a new wedge and cyliner stop spring.
After that I became a believer in the nipple-chain fire theory. AFAIC....grease helps lube the bore to keep fouling soft. It may help prevent a chain fire if using a slightly undersized ball. However, if you're shaving clean rings when seating, I don't see how a spark could get past.
The consensus seems to be that ill fitting nipples are responsible for most chain-fires.
One of the problems is that the Italian pistol manufacturers buy their nipples from a sub-contractor who seems to have trouble holding the tight tolerances required for nipples.
Another problem is that the American manufacturers of percussion caps have never agreed on a "standard cap size" and their caps are slightly different in size from manufacturer to manufacturer. Hence, how well or poorly a percussion cap fits on the nipple of your Italian made revolver is dependent on chance.
So, it is no wonder why we have so many chain-fires because of loose fitting caps. An alternative is to replace your Italian nipples with American made Ampco nipples that are designed to specifically fit the Remmie #10 percussion caps.
I experimented with this some years ago. The only time I got chain fires was using cast bullets (conical or round) that were not a very tight fit, with little or no over ball geese. I always use good fitting caps, however.