I’ve had exactly two chainfires, been shooting replica and original Colts since 1962. A long time anyway. I’ve always used .457 round ball or .454 bullets no matter the revolver. Then a few years ago I got ahold of a Pietta Shooters model. it’s a beautiful pistol. When it arrived I had nothing but 457 round balls on the shelf so I loaded it up and touched it off, the top three chambers fired.
says I. I rotated the cylinder to the next available loaded chamber and
two chambers fired. I had not used grease or wads, just 30 grains of 3f and Remington 10’s. The caps fit just right.
When I loaded the next cylinder I used 50 caliber wads over the powder and haven’t had a chainfire since. Those chambers all measured .4560-.4565 using pin gauges and the gun is a very good shooter so a few years ago I sent a box full of Uberti and Colt cylinders out to Charlie Hahn for reaming to .456”. He does very clean, accurate work and I’m happy but... if I had my druthers I would ream them to .454-.4545” A person could still use .457 round balls and unsized bullets drop at .455-456 from a number of the molds I have.
My experience suggests the phenomenon occurs from the front of the cylinder, but using tight caps and tight projectiles seems to cover the available bases.