btr568, I'm not sure why you are concerned with chain fires with a conversion cylinder! With a conversion cylinder the revolver is loaded with self-contained cartridges, not with "loose" powder and ball. This eliminates the possibility of chain fires entirely.
Chain fires are possible with cap and ball revolvers where each chamber is loaded with loose powder, a ball is pressed in on top, and a percussion cap is applied to the nipple on the rear of the chamber. Most likely chain fires occur when an unfired cap adjacent to the cylinder being fired has either fallen off, exposing the powder in the chamber directly to the flash from the cylinder being fire, or if the adjacent cap fits too loosely on the nipple the flash may ignite the cap itself.