This may be relevant. Extracted from Colonel Samuel Colt's Lecture at the London Institution of Civil Engineers, 25 Nov 1851
Fig 11, plate 1, represents a firearm made by the author, in 1836, to rotate and fire by the continued action of the lever, or by the use of a trigger.
The arms so constructed, consisting of a large number of pieces, and assemble in a complicated manner, were to found to possess many practical disadvantages, arising chiefly from the wish of the Author to construct compact and good looking weapons. His original experiments all been made on the skeleton arms, solely with a view to utility, and in them there was not the liability of premature explosion, from the escape of fire at the mouth of the chamber, or by inter-communication of the ignited detonating camps, but when he enclosed the rear, and the mouths of the rotating chambers, the fire, being confined beneath the shield and the cap, was communicated successfully to the percussion caps, and in front was conveyed into the chambers, so that premature and simultaneous explosion of the charges necessarily took place.
In consequence of these premature explosions it became necessary to remove the shield, from over the base of the chambers, and to introduce partitions, between the nipples, or cones, to prevent the fire from spreading to and exploding the adjoining caps; but this only partially accomplished the object There still remained risk of explosion from the spreading of the fire laterally between the base of the barrel and the face of the chamber. To meet this danger, the metal plate which was attached to the barrel, and projected over the chambers, was removed; this obviated to a certain extent, but did not altogether prevent the simultaneous explosion of the charges for during a trial of the arm, by order of the American Government, an accident occurred, from the simultaneous explosion of two chambers, which induced the Author, after much reflection to give a slight chamfer, or bevel to the orifice of each chamber, so as to deflect, or throw off at an outward angle, the fire which expanded laterally across their mouths. The reason for this alteration was, that when the lateral fire met the rectangular edge of the orifice of the chambers, the angle of incidence being equal to the angle of reflection, the fire was conducted downwards, or inwards to the charge’ but when the flame struck the chamfered edge, it was directed outward away from the charge. Unimportant as this alteration may appear, it has proved so effectual, that if loose powder is placed over the charge, in the adjoining chambers, it is not now ignited when the pistol is discharged. These and other improvements have brought the fire-arm to its present safe and effective condition and the Author believes, that no causality can occur, nor that more than on charge can be fired at one time, if the metal is sound and the arm is properly handled.
