US3429261A - Round of fixed ammunition having improved gun bore erosion characteristics - Google Patents

Description

FIG. vl.

H. ROUND oF FIXED AM M. GOLDSTEIN MUNITION HAVING IMPRovED GUN BORE EROS ION CHARACTERISTICS Filed Oct. 6, 1965 HERBERT M. GOLDSTEIN A TORNEY.

United States Patent 7 'Claims ABSTRACT OF THE DISCLOSURE An improved round of fixed ammunition provided with a vaporizable annular member of erosion protective material surrounding the propellant charge within the cartridge casing, the erosion protective material being composed of a siliconebased, noncarbonaceous material and a vapor depositable metallic material dispersed in the car- Iier material. Upon firing of the round, the protective member is vaporized by the hot propellant gases and the resulting vapors are carried thereby into the gun bore and as an inert laminar layer surrounding such hot gases to protect the gun bore from erosion thereby, and to deposit a sacrificial metallic material film upon the gun bore which film further protects the gun bore from erosion by hot gases and servesto lubricate the passage therethrough of projectiles from subsequently fixed rounds. j'

This invention relates in general to fixed ammunition and more particularly to a round of fixed ammunition having improved gun bore erosion characteristics achieved by means of a self-contained erosion protective material which is arranged to be vaporized by the action of hotpropellant gases upon firing the round in such a manner that the vapors are carried into the gun bore along with the propellant gases and form a laminar layer surrounding propellant gases to protect the gun bore from erosion thereby.

According to a preferred embodiment of the invention, the erosion protective material includes a vapor depositable metallic material dispersed in a carrier material. This further provides improved erosion characteristics in the round because upon firing not only is a laminar layer of protecting vapor formed around the propellant gases passing through the gun bore, but also the metallic material is vapor deposited as a sacrificial film upon the bore surface to further protect it from erosion by propellant gases and to reduce the wear resulting from the passage of projectiles from subsequently fired rounds through the bore. Consequently, the ammunition round represented by the preferred embodiment of the invention is ideally adapted to sustained rapid lire weapons, since the sacrificial metallic film will be continuously renewed. y

The problems associated with gun bore erosion wear are well known in the ordnance art, and increase in se- Verity with propellant charge energy and rate of fire. Throughout the history of firearms, various solutions have been proposed and adopted to reduce the rate of gun bore wear. While some of these solutions have been satisfactory at the time of their evolution, the problem has again become critical because of the high caloric energies and burning temperatures of modern propellants and the trend to ever increasing rates of fire in automatic weapons.

For example, with conventional ammunition rounds, the present useful life expectancy for automatic weapons of the ZOO-1200 rounds per minute class is predicated upon intermittent firing in 3-l5 round bursts, or for approximately 1/2 second per burst. In such weapons, a continuous burst of 2-4 seconds would seriously impair the accuracy of the weapon, and necessitate premature removal from service.

3,429,261 Patented Feb. 25, 1969 ICC With the ammunition round of the instant invention, a typical automatic weapon subjected to firing in 20-40 round bursts may be expected to exhibit wear and accuracy characteristics similar to those which would be eX- perienced if the weapon were tired in 3-8 round bursts using conventional ammunition.

Furthermore, because of the bore protection afforded by the ammunition round of the invention, the accurate life of weapons using such ammunition will extend more closely to the service life of the weapon which will also be increased.

The primary cause of gun bore wear, according to presently accepted theory, is erosion of the bore surface, including such lands or grooves as are provided in rifled bores by the action of the hot propellant gases. These hot gases, by reason of their high temperature and velocity, tend to soften, melt, and remove microscopic portions of gun barrel material from the bore surface each time a round is fired. In general, it has been found that bore erosion begins at the breech end, [more specifically a-t the beginning of the rifling adjacent to the forward end of the chamber, in the case of rifled bores, and at the forward end of the chamber in smooth bore weapons. With the firing of successive rounds, the bore erosion becomes more apparent progressively towards the muzzle end, while also increasing in severity near the chamber end. This is undesirable, particularly in rifles, because it causes enlargement of the chamber to the extent where a substantial chamber pressure loss occurs upon ring subsequent rounds, thereby reducing accuracy and range.

Furthermore, because of the direct contact between the hot flowing propellant gases and the bore surface, a considerable amount of heat transfer to the gun barrel occurs with each round fired. Under conditions of sustained rapid fire, 4the barrel temperature can build up to a level which causes it to deflect of its own weight, or to droop. With a sustained rate of fire which produces a net heat input to the barrel greater than that which can be dissipated by any cooling system provided, the charnber can become so hot as to immediately detonate subsequent rounds introduced therein, thereby leading to explosion of the weapon and injury to operating personnel.

The invention proposes to reduce these undesirable effects resulting from propellant gas erosion experienced with conventional ammunition by generating a laminar layer of non-combustible vapor surrounding the hot propellant gases over the length of their passage through a gun bore. Because of the non-combustible and substantially inert nature of the vapor layer surrounding the propellant gases, there will be substantially no direct contact between the propellant gases and the gun bore surface, and hence the laminar vapor layer will act as an insulator or buffer zone to impede heat transfer to the bore surface and to prevent erosion thereof by propellant gases which would otherwise impinge directly therealong.

In combination with the buler zone type of erosion protection afforded by the laminar vapor layer, the invention provides for the creation of a sacrificial metallic layer which is vapor deposited upon the bore surface by means of the same vapor which forms the laminar layer.

One of the advantageous features of the invention lies in the fact that it can be readily incorporated into substantially any presently known round of fixed ammunition having a cartridge casing, a projectile supported by said casing, a propellant disposed within the casing for expelling the projectile therefrom upon ignition, and means,

' such as for example, a percussion primer for igniting the ber being disposed within the cartridge casing for vaporiyzation by the hot gases resulting from the ignition of the propellant. When the round is -fired in a gun, the vapors from the vaporizable member are carried into the gun bore by the action of the propellant gases and form a laminar layer surrounding such hot propellant gases to protect the gun bore from erosion thereby, such as would otherwise result if these gases were to flow in direct contact with the bore surface.

By using a vaporizable member containing a vapor depositable metallic material dispersed in a carrier material, which is also vaporizable, such as for example, certain silicone compounds, a sacrificial metallic base film can also be deposited upon the bore surface to further protect same from erosion by propellant gases and to reduce bore wear which would normally result from the passage of projectiles from subsequently fired rounds through the gun bore.

For assuring the formation of a laminar vapor film substantially surrounding the propellant gases, the vaporizable member is preferably annular in form, and is disposed within the forward portion of the cartridge casing behind the rear end of the projectile. With such an arrangement, the central open portion of the vaporizable member defines a flow passage for the exit of the propellant gases, and also an ablative surface for progressive vaporization of said member by such gases. The outer peripheral portion of the vaporizable member is disposed in adjoining adherent contact with the interior surface of the cartridge casing to secure said member thereto during vaporization by the propellant gases. In this way, the vaporizable member is retained in its intended position within the cartridge casing for efiicient vaporization, and does not enter the gun bore in the manner of a wad. This feature is particularly desirable in that any portion of the vaporizable member remaining after firing the round is ejected along with the cartridge casing. Also, apart from the thin sacrificial film deposited on the bore, there is no residue formed in either the bore or the charnber as a result of using such vaporizable members.

The vaporizable member can be composed of a silicone compound alone, such as for example, a silicone wax or grease having a melting point about 200 C. so as to be capable of being formed into a definite shape and remaining substantially in such shape when subjected to the ordinary and environmental temperature range associated with the storage and use of ammunition. Preferably, the vaporizable member is formed from a silicone compound carrier material in which a vapor depositable metallic material is dispersed, preferably in finely divided form and substantially homogeneously distributed therethrough. Such a vapor depositable metallic component can be a molybdenum compound such as for example molybdenum oxide or molybdenum disulphide.

A vaporizable member composed of a silicone compound carrier and colloidal molybdenum disulphide dispersed homogeneously throughout the carrier material is considered preferable to most other mixture compositions previously mentioned.

While the exact optimum weight ratio between the vaporizable member and the propellant charge will depend upon several factors, including burning rate, propellant grain type and composition, etc., for practical purposes, in the case of a vaporizable member having silicone carrier and a molybdenum disulphide vapor plating component, a vaporizable member to propellant charge weight range of 0.1 to 5% is satisfactory, and for many propellants, a vaporizable member weighing approximately 1% of the propellant charge will be optimum.

Colloidal molybdenum disulphide having a particle size ranging between 0.01 to 1,000 microns can be used in the vaporizable member of the invention. However, while such a relatively wide particle size range will suffice in general, for the Sake of optimizing the vapor plating feature, a narrower particle size range of 0.05 toy microns is to be preferred.

As Ibetween the relative weight proportion of the colloidal molybdenum disulphide and the silicone carrier which make up the vaporizable member, in general it can be stated that a vaporizable member composition wherein the colloidal molybdenum disulphide constitutes l to 10% of the total member weight will be satisfactory. For colloidal molybdenum disulphide particle sizes Within the range of 0.1 to 20 microns, the molybdenum disulphide preferably constitute 0.01 to 30% of the total weight of the vaporizable member.

In the prior art, numerous attempts have been made to reduce the erosive effects of propellant gases upon gun bores. These have included the use of ammonium carbonate as disclosed by Patten in U.S. Patent No. 1,187,779, wherein the ammonium carbonate produces a cooler gas surrounding the propellant gases. However, ammonium carbonate as used therein tends to produce large quantities of smoke, which would be highly undesirable in most military applications.

U.S. Patent No. 2,131,353 to Marsh discloses various additives for smokeless powder to form a deposit protecting the gun bore against corrosion by humidity and residual combustion products trapped in the bore. While this is quite useful, it does not represent a solution to the erosion problem presented by the propellant gases themselves.

Jacobson et al. in U.S. Patent No. 3,148,620 proposes a series of elaborate measures to form a layer of insulating or cool gases surrounding the propellant gases, such measures including the use of clot-h covered strips, and the coating of the propellant grains with hydrocarbon material. However, such erosion protective measures present problems of themselves because of their use of hydrocarbon materials which oxidize and thereby enter into the over-all combustion product material and energy balance to the extent that the propellant burning characteristics and over-all ballistic performance of the round becomes altered. For example, the coating of propellant grains with a hydrocarbon material will tend to inhibit their burning rate and hence the propellant gas pressuretime relationkwhich establishes projectile ballistics.

As can be :appreciated by the artisan, the erosion protectionA method underlying the invention is not necessarily limited to fixed rounds of ammunition, and can be applied generally to any device, such as for example a rocket motor where hot propellant gases are guided through a passage defined by a material which is 'subject to erosion by such hot gases. In such case, at the entrance to the portion of the passage or nozzle which is to be protected, an annular member of the same type of erosion protective material used in the vaporizable member can be provided. Even with the :absence of a projectile, in such applications, the hot propellant gases `would fiow through y the central open portion of such an annular vaporizable member and form a similar laminar layer of protective vapor separating the hot propellant gases from direct contact with the interior surface of the fiow passage. Such an arrangement will permit the use of materials which are more sensitive to erosion by hot `gases than would otherwise be permitted, and thus would be particularly advantageous in the construction of expendable rocket motors from relatively cheap materials.

It is, therefore, an object of the invention to provide a round of fixed ammunition which has more favorable gun bore erosion characteristics.

Another object of the invention is to provide a round of fixed ammunition as aforesaid which is suitable for more sustained firing bursts in automatic weapons.

A further object of the invention is toy provide a round of fixed ammunition which, upon firing, results in the deposition of a thin film sacrificial metallic layer upon the gun bore surface to further protect same from propellant gas erosion, and to reduce wear thereof occasioned by subsequently fired rounds.

Still another and further object of the invention is to provide a round of xed ammunition as aforesaid which can be readily produced by conventional loading equipment.

Another object of the invention is to provide a general method for protecting the interior surfaces of flow passages from erosion by ihot gases flowing therethrough.

Other and further objects and advantages of the invention will become apparent from the following detailed description and accompanying drawing in which:

FIG. 1 is a longitudinal view, partly in section, of a round of ammunition constructed in accordance with a preferred embodiment of the invention.

FIG. 2 is a longitudinal view, partly in section, of a round of ammunition similar in construction to that of FIG. 1, having a constricted neck cartridge casing.

FIG. 3 is a schematic longitudinal section view of a gun bore through which a round of ammunition of the type shown in either FIG. l or FIG. 2 has been fired, illustrating the arrangement of the laminar layer of protective vapor surrounding the propellant gases, and the deposited sacrificial metal film.

FIG. 4 is a longitudinal view, partly in section of a rocket motor embodying the vaporizable member erosion protection method according to the invention.

Referring now to FIG. 1, the round of fixed ammunition embodying the gun bore erosion protection means according to the invention is provided with a vaporizable member 11 of erosion protective material, preferably a silicone compound, disposed within the cartridge casing 12 for vaporization by hot gases resulting from the ignition of a propellant 13, also disposed within the casing 12 and arranged therein for ignition by a percussion primer 14.

Since the erosion protection afforded by the invention relies upon the creation of a laminar layer of protective vapor surrounding the hot propellant gases, the vaporizable member 11 is preferably annular in form and is positioned within the forward portion of the casing 12, behind the projectile 16. With such an arrangement, the central open portion 17 of the vaporizable member 11 defines a flow passage for the exit of the propellant gases, as is necessary in order to expel the projectile 16 from its original seated position in the casing 12 and out through the gun bore (not shown). Otherwise, the vaporizable member 11 would tend to act like a wad upon firing the round 10, and most likely would not be vaporized in such a manner as to create a laminar vapor layer around the propellant gases.

To prevent such wadding action, the outer peripheral portion 18 of the Vaporizatble member 11 is disposed in adjoining adherent contact with the interior surface 19 of the casing 12. Such adherent contact can be simply achieved by inserting the vaporizable member 11 into the casing 12 and expanding said member 11 radially to provide a press lit along the contact region of its periphery 18 and the surface 19, and thereby secure the vaporizable member 11 to the casing 12 throughout the relatively short period of vaporization by the propellant gases.

As can be appreciated by the annular geometry of the vaporizable member 11, its central open portion 17 also defines an annular ablative surface for progressive vaporization of the member 11 by the propellant gases. Hence, there will be substantially an axisymmetric vaporization of the member 11 with the protective vapors therefrom being carried into the gun bore by the action of the propellant gases.

From FIG. 3, it can be noted that the laminar layer 20 of vapor from the member 11 surrounds the owing core 21 of hot propellant gases, with the outer peripheral boundary of the laminar layer 20 being substantially in contiguous adjoining contact with the bore surface 22 along the length thereof. Although some of the vapor in the layer 20 will be carried out to the muzzle end of the bore surface 22 along with the propellant gases, the progressive vaporization of the member 11 assures that during the entire period of propellant gas flow, the bore surface 22 will be insulated from direct contact with the hot propellant gases by the intervening laminar layer 20 of vapor. Because of the composition of the vaporizable member 11, its vapors are substantially inert to the propellant gases, and thus do not enter into any combustion reaction. Consequently, the vapors of the laminar layer 20 are somewhat cooler than the propellant gases in the flow core 21. Consequently, by insulating the bore surface 22 both from direct physical contact with the propellant gases and from the high temperatures thereof, a considerable reduction in gun bore erosion is achieved, along with a corresponding reduction in heat transfer to the gun barrel per round 10 fired.

As can be appreciated by the artisan, the ammunition round 10 of the invention in its simplest embodiment provides two-fold advantage over conventional rounds in that by reducing the gun barrel heat input per round, a greater number of rounds 10 per firing burst can be tolerated for a given level of permissible barrel temperature, and the gun bore erosion per round 10 fired is markedly reduced.

By using a vaporizable member 11 containing a vapor depositable metallic material, such as colloidal molybdenum disulphide, dispersed in a carrier material, such as a silicone compound, an additional advantageous gun bore protection can be realized. In such case, which represents a preferred embodiment of the invention, the vapors from the member 11 will be carried into the gun bore and form a protective laminar sheath 20 around the propellant gas ow core 21, just as in the case of a vaporizable member 11 without any dispersed metallic material, and such vapors will also carry the metallic material and deposit it as a sacrificial lrn F upon the bore surface 22, thereby providing additional protection against the erosive effects of propellant gases, and particularly in the case of a molybdenum disulphide vapor depositable components, such sacrificial metallic film will also serve to lubricate the passage of projectiles from subsequently fired rounds through the gun bore.

One of the advantageous features of the invention lies in the fact that the vaporizable member 11 can be incorporated into various types of conventional cartridge casings, such as for example cartridge casings 12 having constricted neck portions 23 as illustrated in FIG. 2., Thus,

by no means is the invention limited in its application toA ammunition rounds 10 having straight cylindrical type casings 12 as shown in FIG. l. Likewise, various types of projectiles 16 can be used in such ammunition rounds 10.

In certain respects, a constricted neck cartridge 12 offers a more positive holding of the vaporizable Ymember 11 by reason of the constricted portion 23 which will tend to hold the vaporizable member 11 in its intended position under ablative vaporization by the propellant gases. While a constricted neck portion 23 may appear to present some difficulty in the introduction of the vaporizable member 11' into the casing 12 during loading of the round 10, such difficulty can be easily overcome by molding the member 11 with an original outer diameter which will pass easily through the constricted portion 23 and then by radially expanding the member 11' with a conventional mandrel or pin (not shown) until it is seated firmly against the inside surface 24 of the constricted portion 23, and preferably with a press fit.

The cross-sectional geometry of the vaporizable member 11, 11' can be varied as expedient for various types of rounds 10. However, in all cases, the area of the central open portion 17 of the member 11, 11 must be sufficient to allow the ow of propellant gases therethrough without undue restriction.

As a rule of thumb, a member 11, 11 having a central opening 17 equal an area to approximately 50-75% or greater of the projectile 16 maximum cross-sectional area will be satisfactory insofar as providing a sufficient initial flow area for the propellant gases. It is not practical to further specify the size of the opening 17 because when the round 10 is fired, the area of the opening 17 will rapidly increase as the member 11, 11' is vaporized. Accordingly, the size of the opening 17 can be varied as desired to achieve various vaporization and ballistic characteristics. However, a member 11, 11 without any opening 17 such as a disk (not shown) is not recommended because such a shape would require puncturing by the propellant gases, thereby wasting energy and perhaps resulting in a non-symmetrical ablative vaporization surface.

In any given application, once the total weight and hence the volume of the vaporizable member 11, 11 has been established, its specific annular and cross-sectional geometry can be determined by the application of conventional engineering techniques. For example, by increasing the cross-sectional dimension of the vaporizable member 11, 11 in the direction of casing 12, 12 length, a required member 11, 11 volume can be achieved without the need for any excessive reduction in area of the opening 17 such as would seriously impair the unrestricted liow of propellant gases therethrough.

If desired, the propellant 13 load can be extended into or through the annular opening 17 as is exemplified in FIG. 2, or the propellant 13 can be loaded up to the underside of the vaporizable member 11 as in FIG. l.

Although the vaporizable members 11 and 11 may differ somewhat is cross-sectional geometry, both can be constructed of substantially the same materials. In general, the vaporizable members 11 and 11 are preferably molded from a silicone compound material which is solid or at least semi-solid throughout the normal environmental temperature range which will be experienced by the rounds 10. For this purpose, a silicone compound wax or grease having a melting point above 200 C. will be satisfactory.

Where it is not desired to provide the vapor deposited layer protection feature of the preferred embodiment of the invention, the vaporizable members 11 and 11 can be molded from such a silicone grease or wax compound alone. However, it is preferable to add a vapor depositable metallic component to the vaporizable members 11 and 11', in which case the silicone compound will serve as a carrier to accommodate the dispersion of such metallic component.

In general, it would be undesirable to use most pure metals in powdered form as vapor depositable components, since one of the objects of the invention is to provide a laminar vapor layer which is substantially inert chemically to the hot propellant gases, and because most powdered metals will react exothermically with such gases. Accordingly, the vapor depositable metallic component is preferably a compound of a metallic element, such as for example, molybdenum oxide, or better yet, molybdenum disulphide.

Excellent results can be obtained by using colloidal molybdenum disulphide dispersed homogeneously throughout a silicone carrier component which constitutes the major weight portion of the vaporizable member 11, 11', with the colloidal molybdenum disulphide component being preferably 1 to 10% of the total weight of the vaporizable member 11, 11', For satisfactory vapor deposition of a molybdenum disulphide sacrificial film upon film upon the gun bore, a colloidal molybdenum disulphide component having a particle size within the range 0.01 to 1,000 microns can be used generally, with a narrower particle size range of 0.05 to 100 microns being preferable for most applications.

In cases where the colloidal molybdenum disulphide constitutes 0.01 to 30% of the total weight of the vaporizable member 11, 11 an even narrower particle size range of 0.1 to 20 microns is preferable.

As a general guide to the relative weight proportions between the vaporizable member 11, 11 and the propellant 13 charge, it can be stated that a vaporizable member 11, 11 having a silicone carrier and molybdenum disulphide component total weight equal to 0.1 to 5% of the propellant 13 charge Weight can be used satisfactorily. For a more optimized performance with most propellant 13 charges, a vaporizable member 11, 11 weighing approximately 1% of the propellant 13 charge is recommended.

While the vaporizable members 11, 11' have been described in terms of a silicone carrier and a metallic compound such as molybdenum disulphide colloidally dispersed in the silicone carrier, this by no means implies that other components cannot be added to such a basic vaporizable member 11, 11 composition for the purpose of achieving selected variations inthe characteristics of the laminar vapor sheath 20 surrounding the propellant gas liow core 21, and for depositing various types of sacrificial films F on the bore surface 22.

However, in varying the composition of the vaporizable member 11, 11', it must be kept in mind that no component should be added which would react chemically with either the propellant 13 in solid form or with the propellant gases, or furthermore with any other element of the round 10. Accordingly, the vaporizable member 11, 11 must not contain any carbonaceous material such as hydrocarbons which can react combustibly with the propellant gases and perhaps coat the propellant 13 itself and thereby inhibit or adversely affect its burning characteristics. For these reasons, silicone compounds, which may generally be characterized as analogous to hydrocarbons with silicon atoms substituted for carbon atoms, are ideal, because of their inertness and stability as compared to hydrocarbons such as paraffin, waxes and cellulosic compounds.

In the case of rounds 10 which will be rapid fired in small caliber weapons, a more effective laminar vapor layer 20 can be created by using silicone materials having relatively low stable melting point temperatures, on account of the short propellant 13 burning time in such rounds 10.

Thus, silicone greases and waxes having melting points of approximately 200 C. are preferable in such cases.

The proportions of molybdenum disulphide used can be varied within the aforementioned limits, and perhaps slightly beyond, subject to the general restrictions that for any given round 10 a sufiicient amount of molybdenum disulphide must be provided to result in a vapor deposited sacrificial layer of molybdenum disulphide along the entire bore length, and the amount of molybdenum disulphide used must not be so excessive as to interfere with the combustion of the propellant 13.

Consequently, the optimum proportions of silicone carrier and molybdenum disulphide will depend upon the caliber and intended energy level of the round 10, and to some extent upon the physical characteristics of the weapon in which such rounds 10 will be red.

As to the specific chemical compositions of silicone compounds which can be used as the carrier component, or alone in the vaporizable member 11, 11', it can be said in general, that any vaporizable silicone compound which can be easily molded at room temperature into the required definite annular shape, and which will substantially retain such original shape under the environmental conditions to which the round 10 will be subjected, can be used. For example, silicone compounds and mixtures such as silicone stop cock grease commonly sold by the Dow Corning Company, or the room temperature vulcanizing and potting compounds, RTV-102 and RTV-108 commonly sold by the General Electric Company can be used.

Silicone compounds and mixtures specifically designed for high temperature use, and which are frequently identified by their red color due to their red iron oxide components, are not recommended for use in the vaporizable member 11, 11.

As a general guide, silicone materials used for making the vaporizable members 11 and 11 should have relatively high viscosities, i.e. in the order of 10,000-20,000 centipoise in order to prevent them from flowing out of their original shapes. Low viscosity silicone materials should not be 4used because of the chance that they would ow to the extent of coating the grains of propellant 13 at certain elevated environmental temperatures, and thereby interfere with propellant 13 burning.

Further guidance in the choice of available silicone materials for particular military applications can be found in the U.S. Government publications MIl'rSTD-417 and MIL-R-5847.

As can be appreciated by the artisan, any portion of the vaporizable member 11, 11' which is not vaporized by the propellant gases will remain adherent to the casing 12, 12 and will be ejected therewith in the normal operation of weapons using such rounds 10. Consequently, there is no problem of any residue from the 4member 11, 11 being carried into the bore of the weapon. In this respect, the manufacture of the ammunition round 10 of the invention becomes less critical in that no extraordinary care need be taken in controlling the weight of each vaporizable member 11, 11.

Apart from the construction of the ammunition rounds 10, the invention also teaches a general method of protecting tubular conduits from erosive action of hot gases passed therethrough. Thus, the erosion protection method of the instant invention is generally applicable to blank cartridges, rocket motors, etc., which involve the ilow of hot gases through a conduit such as a gun bore or nozzle without the expulsion of any projectile 12 as in the case of the ammunition rounds 10.

According to the invention, a conduit can be protected from erosion by hot gases flowing therethrough by passing such gases through an annular vaporizable member of erosion protective material similar to that of the members 11, 11. For example, in the rocket motor 25 shown in FIG. 4, a vaporizable member 11" is positioned at the inlet of a nozzle 26 to protect the interior surface 27 downstream of said member 11" from erosion by hot propellant gases flowing therethrough from a combustion chamber 28 wherein a propellant 29 is burned.

In this particular example, the vaporizable member 11" functions in substantially the same manner as the members 11, 11', to provide a laminar layer 20 of inert vapors surrounding the propellant gases for protecting the nozzle 26, interior surface 27 from erosion thereby.

If desired, a vapor depositable metallic component can be dispersed within the vaporizable member 11" as in the case of the members 11, 11' to provide further erosion protection for the interior surface 27 in the form of a sacrificial lm continuously deposited thereupon and hence continuously renewed during the life of the member 11".

While the vaporizable member 11" may not be practical forv long burning time rocket motors 25, there are many rocket motors 25 of the one-shot, expandable type wherein .the provision of a vaporizable member 11" for propellant ow erosion limiting would permit an advantageous reduction in over-al1 structuralweight.

From the foregoing, it can be appreciated that the in stantvinvention affords both a general method for reducing and limiting the deleterious effects of erosion by hot flowing gases, and a round 10 of fixed ammunition constructed on the basis of the principles underlying such method. As will become apparent to the artisan from the description of the invention herein given in terms of illustrative examples, the invention is susceptible of other obvious embodiments and is intended to be limited in scope only by the following claims in which I have endeavored to claim all inherent novelty.

What is claimed is:

1. In a round of xed ammunition having a cartridge casing, a projectile supported by said casing, a propellant disposed within said casing for expelling said projectile therefrom upon ignition, and means for igniting said propellant, the improvement which comprises an yannular vaporizable member composed of a noncarbonaceous carrier material and -a vapor depositable metallic material, said carrier material being a silicone compound, and vapor depositable -metallic material being molybdenum disulphide in colloidal form and substantially homogeneously dispersed throughout said silicone compound carrier material, said annular vaporizable member being disposed within said cartridge casing in surrounding relation to the propellant for vaporization by hot gases resulting from the ignition of vsaid propellant to form vapors inert to said hot gases and which are carried into the gun lbore bythe action of said hot gases and surround said hot gases to protect the gun bore from erosion thereby, and deposit a sacrificial metallic material film upon the gun bore to further protect same from erosion by such hot gases and to lubricate the passage of projectiles from subsequently tired rounds through the gun bore.

2. The improvement according to claim 1 wherein the total weight of the silicone carrier and molybdenum disulphide components of the vaporizable member is 0.1 to 5% of the propellant charge weight.

3. The improvement according to claim 1 wherein the total weight of the silicone carrier and molybdenum disulphide components of the vaporizable member is approximately 1% of the propellant charge weight.

4. The improvement according to claim 1 wherein said colloidal molybdenum disulphide has a particle size within the range 0.01 to 1,000 microns.

5. The improvement according to claim 1 wherein said colloidal molybdenum disulphide has a particle size within the range 0.05 to microns.

`6. The improvement according to claim 1 wherein said colloidal molybdenum disulphide has a particle size within the range 0.1 to 20 microns, and wherein said colloidal molybdenum disulphide constitutes 0.01 to 30% of the total weight of the vaporizable member.

7. The improvement according to claim 1 wherein said colloidal molybdenum disulphide constitutes 1 to 10% of the total weight of the vaporizable member.

References Cited UNITED STATES PATENTS 1,187,779 6/1916 Patten.

2,779,281 1/ 1957 Maurice 102.-39 3,148,620 9/1964 Jacobson et al 102-38 3,204,558 9/ 1965 Jacobson et al 102-38 3,209,689 10/ 1965 McLennan 102-38 3,282,215 11/ 1966 Roth 102,-38

ROBERT F. STAHL, Primary Examiner.

\U.S. Cl. X.R. 60--218; Z39-265.15

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