I can only think of a few more questions to be asked on this topic; here's the first.
Gomer or cylinder shaped powder chamber; is one superior to the other?
My Dom dictator is concave ball seat cylinder powder chamber.
My scrap yard Mortar has a flat ball seat. I am going to make a tapered Gomer style chamber for it.
"Gomer chamber. A chamber in the bore of a howitzer, or mortar named after the French Officer who first used it. It was at the extremity of the bore, cone shaped, rounded at the end so that the charge could be as compact as possible. The shell rested on the mouth of this chamber and the charge acted directly upon it."
"Gibbon's Artillery Manual
Chamber.-- When a light piece is intended for throwing large and heavy projectiles, the effect of recoil may be lessened by employing small charges of powder; but as they would be difficult to manage, and would form but a small mass retained with difficulty in its proper place in the gun, a cavity called a chamber is made in the bottom of the bore, designed to keep the powder together in its proper place, and by keeping it more confined, increasing its efficiency. There are three kinds of chambers: the cylindrical (A), Fig. 13, conical (B), and spherical (C).
CYLINDRICAL
GOMER
SPHERICAL
Cylindrical .-- In the first, the bottom of the bore at the mouth of the chamber is formed of a portion of a sphere, so that the projectile closes the mouth of the chamber. This is the chamber used in our different howitzers, and in the eprouvette mortar. It is, however, joined to the bore in the way above described only in the eprouvette, and in one of the howitzers (the 8 -in. siege).
In the other howitzers it is connected by means of a conical surface, the junctions being rounded off to prevent being worn away by the action of the powder. Cylindrical chambers, when narrow and deep, give greater ranges than shallow wide ones, which do not confine the powder so much, but as in the former the gas acts on but a small segment of the projectile (usually hollow), it sometimes breaks it; and, for this reason, too great a depth in cylindrical chambers is avoided.
The Gomer chamber (after its inventor) consists of the frustrum of a cone connected with the bore by a portion of the surface of a sphere. This kind of chamber is considered the most .advantageous for mortars, and is used in most of ours. Being large at the mouth, it allows the powder to act on an entire hemisphere of the projectile, and no risk is run of breaking it. It, however, gives a less range than either of the others, but its capacity is greater.
The spherical chamber consists of a sphere, joined to the bore of the piece by means of a small cylinder which serves as a channel to the gases. As this cylinder decreases in diameter, the gas fines more difficulty in escaping, and greater force is developed.
This chamber, however, is even more objectionable than the cylindrical one, from its liability to break the projectiles, although it gives the greatest range of the three chambers. This chamber is in the first place hard to make, and, in. use, soon becomes foul, and is very difficult to clean out. It is now entirely given up."
"Maj. Joseph Robert’s Hand-Book of Artillery, for the Service of the U.S. (Army and Militia.) 1863
6. Why is a mortar constructed with a chamber?
In consequence of employing various charges, some very small, it becomes necessary to use a chamber to concentrate the charge as much as possible, so that the shell may be acted on by the entire expansive force of the powder.
7. What form of chamber is given to mortars?
That of a frustum of a cone. The bottom is hemispherical in the sea-coast mortar. In siege mortars it is a plane surface, the angles of intersection being rounded in profile by arcs of circles.
8. What is this form of chamber called?
Gomer Chamber.
9. What is the advantage of the conical over the cylindrical chamber?
Cylindrical chambers are objectionable, as the projectile is frequently broken in consequence of the small surface exposed to the action of the charge. This defect is obviated by large chambers, and particularly by those that are conical, in which the charge is expended upon nearly a hemisphere.
10. How are mortars designated ?
Usually by the diameter of the bore in inches.
11. How are mortars mounted?
On beds of wood or iron. Those for the new model mortars are made of wrought iron."
Most period writings state that the cylindrical chamber fired the projectile a further distance, and that the Gomer chamber charge was less likely to rupture the shell when fired. The asset (if true) attributed to the Gomer chamber doesn't really apply to our purposes, since we're going to be firing solid projectiles. I can't find any literature that claims either chamber type was more accurate than the other.
Douglas; are you planning on giving your mortar a Gomer chamber just for historical accuracy?
From a machinist's viewpoint: Would it be a much more difficult task to fashion a Gomer chamber?