Well, I am working from memory so cut me some lack but as I recall the last time I had this discussion one guy used a propane torch and put powder and wads in all the chambers but no caps on the nipples. A quick wrist flip of the torch over the nipples blew all the chambers but the wads didn't result in any firings. Several things were deduced. First, if the wads saved the day then even if the ball is poorly sized or the chamber is out of round- if the wad is used- that ought to help a lot. Second, if a cap on an abutting chamber is loose or gets knocked off on recoil, hot gases could easily ignite the chamber.
As I recall most of these chain firings were really just one other chamber going off, not all six. Usually the faulty chamber was abutting the one lined up with the barrel.
As far as forcing cones, etc deflecting flames into the chamber ends- that could be but the pepper box pistols were notorious for chain firings and they had no forcing cones, etc.
Probably the biggest surprise was that nearly all chain firings occurred on the first cylinder loading for the day- we couldn't figure that one out but surmised that the only difference would be oil still around the caps- maybe capillary action of some sort caused hot gases to get sucked through the nipples.
In any event we never did come up with one cause- we figured oily nipples, loose fitting caps, poor fitting balls and/or chambers out of round.
P.S. on the loose fitting balls, one guy thought on recoil a loose fitting ball could actually slide forward enough that gases blew the powder charge- may sound funny but in many of these chain firings the damage is surprisingly minimal- which might be the case if the ball is already mostly out of the chamber when the powder blew.
Last edited by davem; June 19, 2010 at 02:59 PM.