At one time, Col. Colt did chamfer the mouths of the cylinders chambers.
In fact, he had a Patent on chamfering the edge.
If you find his Patent you will find that it had nothing to do with loading roundballs or bullets.
In the design, the chamfer was quite large and its intended purpose (according to the Patent) was to deflect the flame from the firing chamber away from the neighboring chambers where the ball seats against the chambers bore.
This was intended to reduce the possibility of a chain fire.
Quoting from
"On the application of machinery to the manufacture of rotating chambered-breech firearms and their peculiarities", by Col. Samual Colt
"...so that premature and simultaneous explosion of the charges necessarily took place. In consequence of these premature explosions it became necessary to re move the shield from over the base of the chambers, and to introduce parti tions 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 bevil, to the orifice of each chamber, so as to deflect, or throw off at an outward angle, the ftre which expanded laterally across their mouths. The reason for this alteration was, that when the lateral Are 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 outwards away from the charge. This action is shown in woodcut (Fig. 1), and 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 casualty can occur, nor that more than one charge can be fired at one time if the metal is sound and the arm is properly loaded."
(page 8 of 36 in this link):
https://books.google.com/books/reader?id=QnkDAAAAYAAJ&printsec=frontcover&output=reader&pg=GBS.PR3
It might be noted that this method of addressing the chain fire issue was early in the creation of the Colt pistol (1836-1842).
By the time the Colt 1851 Navy was being made, most of the cylinders did not have chamfered chambered mouths.
