This is what Colt said about loading the revolvers his company made.
First explode a cap on each nipple to clear them from oil or dust, then draw back the hammer to the half-cock, which allows the cylinder to be rotated; a charge of powder is then placed in one of the chambers, keeping the barrel up and a ball with the pointed end upwards without wadding or patch is put into the mouth of the chamber, turned under the rammer, and forced down with the lever below the surface of the cylinder, so that it cannot hinder its rotation
(care should be used in ramming down the ball not to shake the powder from the chamber, thereby reducing the charge).
This is repeated until all the chambers are loaded. Percussion-caps are then placed on the nipples on the right of the lock-frame, where, by drawing back the hammer in the full-cock
the arm is in condition for a discharge by pulling the trigger; a repetition of the same motion produces the like results with six shots without reloading.
-----------------
With properly fitting caps there is little danger of a chain fire as long as the caps are fully seated on the nipples and the ball/bullet sheared off a ring of lead while it was being rammed into the chamber.