Singing Bear:
I too have heard that the original guns had tapered chambers. However, I've never seen anyone offer evidence of this, through chamber casts or measurements. Be interesting if someone with original cap and balls could do this.
I'm not one of those who believes that flashover begins at the front --- unless the chamber is out-of-round, which I believe is a rare defect.
Back in the early 70s I had a multi-ignition occur on two separate occasions with my cheap, brass-framed, Italian-made copy of the 1851 Navy in .44 caliber.
In the first incident, the chamber in line with the barrel went off, as planned. However, the chamber to the right of it and directly below it also went off. Three chambers are once!
It was immediately apparent that something out of the ordinary had happened because the blast and recoil were so much greater.
The ball in the chamber to the right of the barrel went flying off God knows where. The ball at 6 o'clock rammed into the rammer and stopped. No damage, though.
Sometime later, the same thing happened. This time, the ball damaged the rammer. I gave the gun to a gunsmith friend for parts.
The load was with DuPont black powder, .451 inch ball and Crisco smeared over the ball. Caps were just placed on the nipples, without being pinched into an oblong shape so they'd cling to the nipple.
That's how I loaded it back then, but no more.
Today, I still use black powder but I use a larger ball of .454 or 457 inch in my .44 revolvers, and .380 inch in my .36-calibers. I use a well-lubricated felt wad between ball and powder and rarely use lubricant over the ball. Caps are matched as close as possible to the nipple, but still pinched into an oblong size so they don't fall off or are jarred off from recoil.
Since adopting this loading procedure, I've never had another multi-ignition incident.
Colt's old instructions don't mention a lubricant or lubricated wad but it is known that soldiers and frontiersmen sometimes dripped candlle wax or beeswax over the seated ball and capped nipple to make the loads water-resistant. I suspect that the wax over the ball helped lubricate it too. Whether it prevented chain-fires from flashover at the front, I doubt.
Unless the chambers are out-of-round, I just don't see how the flash can get past a tightly seated ball clinging to every surface of the chamber.
But an out of round chamber? Yeah, I can see that.
Trouble is, I've never seen an out of round chamber. I'm sure they exist because tools can get out of alignment or chatter at the factory; I've just never seen one.
For my money, multi-ignitions or chain fires begin at the rear, when a cap is loose or absent from a charge.
