I do not have personal experience with cap-and-ball revolvers. I have only a muzzle loading rifle. That said, I read a very detailed post on another forum in which the writer talked about the grease being a great path for chain fires. Instead, he chamfers the opening to each individual bore in the cylinder. That way, the ball gets swaged into place, eliminating the need for any other material. Using this method, the write-up said he had never experienced a chain fire accident. Just a thought, which would appear easy enough to verify.
I have been shooting cap and ball revolvers for over 40 years and I put a little beeswax cookie (50/50 beeswax and Crisco), cut out with a .45 LC case, on top of the powder before seating the ball. Lubes very well and never had a chain fire.