US2620732A - Mortar charge - Google Patents

Description

Dec. 9, 1952 c. N. HICKMAN 2,620,732

MORTAR CHARGE Filed Nov. 29, 1944 CLARENCE N. I-QIICKMAN Patented Dec. 9, 1952 TENT MORTAR CHARGE Application November 29, 1944, Serial No. 565,645

3 Claims. 1

The invention described herein may be manufactured and used by or for the Government, for governmental purposes, without the payment to me of any royalty thereon.

Thi invention relates to ordnance and more particularly to a novel charge for mortar ammunition improving the pressure travel relations within the mortar to provide an increase in the velocity and maximum range of its projectile.

It is well known that the conditions of loading in guns necessary to obtain a maximum velocity should be such that the projectile will commence to move within the barrel of the gun after but a small portion of the powder has been consumed. This movement of the projectile increases the volume of chamber occupied by the powder gases, hence it becomes necessary to have increasingly larger quantities of gas liberated as the projectile moves. That this result may be attained, a progressive burning powder has been used in the prior art to provide the increase in burning surface necessary to produce an increase in the quantity of gas liberated, preventing the pressure within the gun chamber from falling ofi too rapidly with the movement of the projectile down the barrel.

I have been actively engaged in internal ballistics studies on the 4.2" chemical mortar, particularly concerning the eifect upon range of variations in the propellant web size, density of loading, quantity of the igniter, etc. These studies have clearly indicated the desirability of a progressive powder for the chemical motar. The 4.2" chemical mortar is a rifled, muzzleloading weapon, the projectile of which is stabilized in flight by rotation. The propellant charge in the form of square sheets of a double-base powder is secured to the ignition cartridge container by being strung thereon in bundles. The bundles are provided so that a portion of the propellant charge may easily be removed to provide for a decrease in range. It is accordingly very diificult to obtain a progressive powder for the mortar since the configuration of the grains providing the increase in surface as the burning proceeds is not particularly adapted for attachment to the projectile. I have set out to attain a progressive burning charge for these chemical mortar shells and such is the primary object of this invention.

As a result of my experiments with the various loadings of the 4.2" chemical mortar, I discovered that the high pressure developed by the initial burning of a portion of the propellant could be utilized to seal the path of the flame leading to other portions of the propellant charge. This discovery led directly to the development of a special charge for mortars which would simulate th effect of a progressive charge made up of individual progressive burning grains without the necessity of resorting to peculiarly configured grains which are expensive to manufacture and diflicult to secure to the mortar shell. This invention consists, therefore, of a charge for mortars made up into two parts. The first part, comprising a stack of small diameter discs, is ignited by the ignition cartridge and has an initial burning surface suificient to provide a pressure as high as tolerable for the small initial chamber. The second part of the charge is also disc shaped, but of a larger diameter and is snugly fitted into the mortar barrel. The high pressure developed by the burning of the first part of the charge packs the discs comprising the second part of the charge against the base of the projectile moving both the propellant discs and the projectile forward. After a slight delay, the layers of the second charge begin to burn progressively and thus liberate additional quantities of gas to keep the pressure up as the chamber is increased in size. The web thickness of the first part of the charge may be greater than that of the second part and the Webs of the second part of the charge may decrease in thickness in the direction of the burning or towards the base of the projectile to permit completion of burning of the two parts of the powder charge simultaneously.

In the drawing accompanying this invention disclosure I have illustrated by av single figure a longitudinal sectional view of a mortar barrel showing in place within the barrel a projectile provided with the special charge of this invention.

Referring now to the drawing, the mortar barrel indicated generally at 10 has a firing pin I I, protruding inwardly of the barrel from the breach end 12. The mortar shell [3 has an ogive front portion and a base portion, the latter being provided with a cup shaped annular disc 14 of soft metal, of a diameter equal to the diameter of the base portion. Under the action of the powder gases liberated by the burning propellant charge indicated generally at 20, the flange of this annular disc is forced outwardly in the rifling groove of the barrel ID, to seal the chamber l6 and serve the same function as the rotating band of other projectiles. The special propellant assembly of this invention illustrated generally at 20 comprises a plurality of laminated discs of non-hygroscopic powder, preferably ballistite, each of which is provided with a single axial and concentric perforation to permit the propellant laminations to be secured to the projectile [3 by being fitted over a perforated tubular tail portion ll, adapted to contain the ignition cartridge I5. These propellant laminations are held in place by the nut l8 threaded on the end of the tubular cartridge container 11.

As is illustrated, the propellent charge is made up in two parts, designated by the reference numerals 2| and 22. The part 2| is made up of a plurality of relatively thick web grains in disc form having a diameter sufiicient to provide for an initial burning surface to give the desired ini tial pressure within the chamber I 6. As illustrated in the drawings; the openings I9 drilled through the cartridge container I! are confined to the portion of the ignition cartridge which supports the part 2! of the powder charge. The part 22 of the powder charge is made up of a plurality of laminated propellant grains which are disc shaped and of a diameter substantially equal to the outer diameter of the shell 13. The disc 23 of the part of the propellant charge 22 is of a web thickness less than the web thickness of the discs comprising the part 21 of the propellant charge and the remaining discs of propellant material which are supported forwardly in the direction of the base of the projectile H are of increasingly smaller web thickness so that the burning of both parts 2| and 22 of the powder charge 26' may be completed simultaneously. In operation, the projectile l3 with its powder charge 20 is loaded into the barrel It of the mortar from the muzzle end, and is permitted to fall freely within the barrel. Upon engagement of ignition cartridge with the firing pin H the part 2| of the propellant charge 20 is ignited, since this part alone is exposed to the ignition flame issuing from the igniter composition through the drilled openings ill. The high pressure developed by the burning ofthe part 2! of the charge 20 acts upon the propellant lamination 23 of the part 22 of the charge to cause the propellant laminations comprising the part 22 to be packed tightly against the base of the projectile 13 with the result that both the projectile and the propellant laminations 22 will be moved forward within the barrel. After a slight delay, the flame from the burning propellant 2! will have burned through the thinner web propel lant lamination 23 and will have ignited the next adjacent lamination; This progressive burning of the stacked laminationscomprising the part 22 of the propellant charge may be increased by providing other ignition paths within the stack of propellant discs. For example, a number of holes may be punched in each of these discs which overlap to provide for the progressive ignition. In those instances wherein the delay is not sufficiently long some suitable insulating or inhibiting material may be used to cover the exposed surface of the propellant lamination 23. It is thus evident that there are many ways in which the progressive ignition may be accomplished. The chief idea of this invention, which is novel and to which I lay claim, is that the high pressure developed by a burning of a part of the propellant charge is utilized to seal the ignition path leading to the other propellant laminations which go to make up the total charge. Obviously, I do not wish to be limited to propellant web size as shown in the drawings. It being understood that the drawing is for illustrative purposes only and not for limitation. Reference for this latter purpose being had to the accompanying set of claims.

I claim:

1. In combination a projectile for a muzzleloaded mortar, including an ogive front portion, a base portion having a tubular ignition cartridge holder secured thereto, a propellant charge supported on said holder comprising a first and second part, an ignition cartridge in said holder for igniting said first part, said first part of said propellant charge comprising a plurality of disclike sheets of propellant material. of a diameter substantially less than the diameter of said projectile said second part of said propellant charge comprising a plurality of disc-like sheets'of propellant material of a diameter equal substantially to the diameter of said projectile supported on said holder to provide a snug fit with the mortar barrel whereby the high pressure developed by said first part will pack the laminations of said second part tightly against the base of said projectile to temporarily seal the flame path to the laminations of said second part, so that the laminations of said second part will be progressively ignited.

2. The combination defined in claim 1 above, wherein said propellant sheets of said first part each have a web thickness greater thanrthe web thickness of said propellant sheets of said second part; 7

3. The combination defined claim 1 above, wherein the web thickness of said propellant sheets of said second part are increasingly smaller toward the base of said projectile. V V CLARENCE NI-IICKMAN.

REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS Number Name Date 1 1,790,873 McBride Feb.'3, 1931 2,069,794 Woodberry Febf9, 1937

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