Improved case shot “Discharged in the line of flight”: Hotchkiss projectiles, Part 4

Time for another installment on projectile development, and we were working through the Hotchkiss-types.  In the last post about Hotchkiss, I detailed Patent Number 35,153, in which Benjamin B. Hotchkiss attempted to work around issues with packing case shot for rifled projectiles.  The key to that patent was the material used to fix the shot in place within the cavity of the shell.  However, even that was not perfect.  (And let me also say that Patent Number 35,153 appears not to have been used beyond tests.  To my knowledge, no surviving Hotchkiss projectile is marked for the patent or appears to have incorporated the components of the patent.)

The problem left unaddressed was the scatter of the shot when the projectile burst.  Tests and field experience with smoothbore case shot gave a level of predictability to performance.  But the physics involved with rifled projectiles negated those old rules of thumb.  To solve this “payload ballistics” problem, Benjamin B. Hotchkiss advanced Patent Number 38,359:

Hotchkiss_Patent_38359

Right off the top, we see Hotchkiss had collaborators here – Charles W. Smith and G.H. Babcock, both from New York City, along with, Charles A. Hotchkiss. These names and their context are somewhat murky to me.  Charles A. Hotchkiss was likely a relative of Benjamin, and also lived in Sharon, Connecticut.   I have never been able to narrow down Smith’s background.  However, Babcock is possibly George Herman Babcock who is better known for invention of safer boilers and his firm of Babcock & Wilcox. Babcock did work on naval shipbuilding projects during the Civil War, placing him in Mystic, Connecticut.  And Babcock is associated with post-war ordnance patents. Still, only associations based on initials.   While not something to say is “confirmed,” the involvement of someone with an interest in the dynamics of gasses under pressure is intriguing.

While the “who” has some interesting gaps to resolve, the “what” is spelled out in the patent application.  The new design aimed to focus or direct the force of the charge so as to drive the payload (balls) out of the shell in a predictable pattern.  And we see, just from the illustration, this required some substantial changes in construction.  The basic design resembled “an ordinary ‘Hotchkiss shell’” on the outside (labeled “A” on the diagram), but cast with a different interior cavity.  Specifically:

… divided into two parts by the plate B, which rests loosely upon the shoulders a a, prepared for that purpose.  The foremost of these cavities is filled with balls C and the other with powder D, the plate B serving to divide the same and confine each to its proper place.

A tube (labeled “E“)  extended from the fuse (the seat of which is labeled “F“) to the plate, thus allowing connection between the fuse and powder.  Lastly, the inventors created an interior “weak spot” to facilitate the action of the projectile:

The form of the cavity is such that a weak line, G G, is left near the point of the shell, which weak line will first give way to the force of the explosion and allow the balls C to be projected from the shell, much in the manner of grape from a cannon, directly in the line of flight, or at a comparatively small angle therewith.

That sounds good, but looks like it would be difficult to put the plate in place.  Right?  Well, “plan A” for constructing this type of case shot:

In constructing our improved shell we cast the body A with the cavity therein, in the usual manner.  The plate B is too large to enter at the fuse-hole, and we therefore insert it int the core, which forms the cavity, and when the core has been removed in the usual manner the plate B remains and falls into its place upon the shoulders a.

Ah… so construct the plate, put it into the casting mold (usually sand).  When all has cooled, the sand is removed thus leaving the plate loose within the shell. Alternatively, the inventors indicated the cap of the shell, above the line G G, could be cast separately and threaded for attachment.  Such would allow placement of the plate and other interior arrangements.  Let’s call this “Plan B” for purposes of discussion.

But recall from earlier discussions the need to protect the powder from any sparks caused by the friction between the balls and the shell.  The plate did provide some separation, providing a “bulkhead” against sparks reaching the powder cavity.  But that would not prevent powder slipping forward during handling.  A better seal was needed.  Thus:

A washer, I, of cloth or other suitable material, is placed between the plate B and shoulders a a, to serve as a packing to prevent the powder from sifting through the joint among the balls C. Were it not for this packing I, the powder would be liable to enter between the plate B and its seat a and become ignited by the sudden friction occasioned by the discharge, thus producing a premature explosion, to the great danger of those in the vicinity of the gun.

But… now we have the problem of placing a cloth washer, or gasket, over the plate!  If constructed using “Plan B” this is easy enough.  But for “Plan A”, the inventors called for the washer (“I”) to be gummed, inserted through the fuse hole, then worked onto the plate.  So the “Help Wanted” ads would specify “Prefer persons with small hands and excellent dexterity!”

With the plate in place, the tube was inserted through the fuse hole.  After that the balls were loaded.  A plug was used during transportation.  When readied for use, that plug would be replaced by a fuse.  And upon firing, the case shot would perform as such:

When the fuse F has been consumed, the powder D is ignited and tends to rupture the shell; but in consequence of the form thereof the point is first blown off at the weakest line G, and the balls C are projected forward with an increased velocity, the rotary motion of the shell serving to scatter them sufficiently for causing them to act over the required area.

The inventors allowed that different types of effects were possible, such as having the case shot explode, say, on contact.  But….

… the main effect is intended to be derived from the bullets C, the shell A serving, mainly, as a means of conveying them to their destination, and as a mortar from which they are discharged by the explosion of the charge, the bullets receiving a fresh impetus at the expense of that of the shell.

The application went on to say this effect was very important.  Normally, at long range the fragments of case shot would only carry the energy imparted from the initial firing from the cannon.  But this improved design would have a secondary burst that would impart additional energy, thus making the balls more lethal on the intended target area.

One additional specification mentioned in the patent application applied to the plate.  The plate had to be strong and well supported.  Otherwise the balls would crush into the powder cavity.  Therein lay the “uniqueness” of this patent application:

We are aware that shells have heretofore been proposed in which the charge of bullets were placed in front of the charge of powder, with the intention of causing them to be discharged in the line of flight; but as such shells were proposed to be constructed the inertia of the bullets would have so completely crushed the powder as to render their explosion very improbable.

This improved design had much to offer and in most respects was successful.  A great number of recovered Hotchkiss case shot use this type of construction.  Jack Melton, of The Artilleryman Magazine, passes along this sectional view of a deactivated Hotchkiss:

hotchkiss_cutaway_view

We see all the elements of the original Hotchkiss patent – body, sabot, and cup. And we see the elements of this new design for case shot.  Not mentioned in the patent, but called out here, is a nail in the powder cavity used to align the mold.  Note also the size of the tube in the 3-inch case shot, being shorter than that shown in the patent diagram. That is due to the size of the adapter used for the fuse.  Different types of fuses might be suggested for the case shot.  But the most likely would be a time fuse, which would be ignited by the flame from the cannon’s propellant charge.

Now let us step back and consider how this particular projectile behaved in the gun and exactly how such a time fuse would function.  When the lanyard was pulled, the friction primer set off the propellant charge.  The explosion of the propellant pushed the cup forward and forced the lead ring into the rifle grooves.  With that, the bore was sealed so as to impart the rifling onto the projectile.

So… if the propellant charge was to light the fuse, that had to occur within the fractions of a second between the propellant ignition and the lead ring expansion.  A very tight window.  And without the fuse activated, the case shot was for all intents just a solid bolt going down range… not useful for the situations case shot was selected.  So there was a need for something to improve that narrow window in which the propellant could ignite the fuse.

Look to the left side view of the cutaway – “one of three flame grooves“.  Such brings us to the next Hotchkiss patent, which sought to improve reliability of the fuse ignition.

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