Ammunition with protective surface layer and method of making same

A protective surface coating for ammunition having no cartridge casing and ammunition having a combustible cartridge casing. A body of highly porous nitrocellulose is permeated from the outside with a polymer carried by a solvent to form a binder for the body. A layer of metal platelets containing air-pockets is bound to the body with a binding polymer. The metal platelets are covered with an outer coating of a rapidly curing resin. The protective coating is used to prevent the penetration of moisture into the porous cartridge casing or into the powder mass itself and to provide improved stability to heat and flames.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an improved ammunition having a body 
covered with a protective layer and to a method of making same. 
2. Description of the Prior Art 
It is known to provide protective coatings for nitrocellulose ammunition 
cases. 
For example in German published application No. 1 912 727 there is 
disclosed a porous, combustible casing made out of a swellable, 
expandable, natural or synthetic polymer or a derivative thereof which 
acts as a barrier. This barrier layer in turn, after its solidification, 
is provided with a moisture-proof, protective layer. 
Published German application No. 1 578 062 discloses a combustible 
cartridge having no housing with a coating consisting of a highly 
combustible film, the film containing a mixture of dyes, pigments, or 
metal powder (for example aluminum or zinc). J. Brzuskiewicz in U.S. Pat. 
No. 3,987,731 discloses a porous combustible cartridge case containing 
nitrocellulose, reinforcing fibers and a resinous binder, which is 
rendered resistant to water and oil by coating the surface with a 
composite coating containing an undercoating of polyvinyl alcohol and a 
top coating of a copolymer of vinylidene chloride and acrylonitrile. 
In general, there is the requirement regarding ammunition having a 
combustible cartridge casing that an uncontrolled premature ignition of 
the ammunition due to contact with hot substances or parts either inside 
the weapon or outside the weapon is prevented while simultaneously not 
preventing the combustion of the ammunition at a preselected time. 
Additionally, it is desired that the protective surface coating shall 
provide moisture resistance and waterproofing as well as protection 
against deterioration resulting from fungi or contaminating oil. 
The afore-described properties of the protective surface coating and 
particularly the ease of combustibility providing complete combustion 
without residues and the simultaneous presence of flame retarding 
characteristics are not met satisfactorily in any of the prior art 
ammunition. For example, the protective coatings of the German published 
application Nos. 1 912 727 and 1 578 062 have satisfactory moisture 
resistant and waterproofing characteristics, but they are flammable and 
therefore do not solve the safety problem attendant upon combustible 
cartridge casings and ammunition having no cartridge casings. 
The ammunition described in U.S. Pat. No. 3,987,731 uses as a starting 
material fiber reinforced nitrocellulose employing in particular acrylic 
fibers and as a binder polyvinylacetate resin. Nitrocellulose having a 
nitrogen content of up to about 12.6 weight percent has the disadvantage 
of dissolving easily when contacted with a dissolving solution such as 
with a xylene solution. This nitrocellulose with relatively low nitrogen 
content has no oxidation reserve and therefore one has to expect the 
formation of residues upon firing. The acetate of the binder of U.S. Pat. 
No. 3,987,731 forms only a physical bond with the nitrocellulose material, 
is also susceptible to solvents, and there is a considerable transmission 
of such a casing. 
According to U.S. Pat. No. 3,987,731 a first layer of polyvinyl alcohol 
primer lacquer is employed and then a layer of polyvinylidene chloride 
acrylonitrile copolymer lacquer. The first layer is insoluble in the 
solvents of the polyvinylidene chloride acrylonitrile copolymer lacquer 
and for obtaining the heat protective effect such a large amount of 
aluminum is combined with the polyvinylidene chloride acrylonitrile 
copolymer as to make combustion without a residue very doubtful. 
Furthermore, the combustion of the polyvinylidene chloride results in 
chlorine and/or hydrochloric acid and their derivatives which can increase 
erosion of the container of the cartridge. The weight of the layer amounts 
to more than 1.1 to 6 weight percent of the total weight of the 
ammunition. Such an amount is excessively high and constitutes a serious 
drawback. The large amount of material forming the coating is not burned 
without any residue during firing. 
The protective coatings of the state of the art, for the reasons enumerated 
hereinabove, have not satisfactorily solved the opposed and contradictory 
requirements that are involved, i.e., no satisfactory compromise has been 
found between the necessary protective effect desired and the external 
influence of heat and the necessary requirement of complete combustion 
without residue during the firing of the shell. 
SUMMARY OF THE INVENTION 
1. Purposes of the Invention 
It is an object of the present invention to provide a protective surface 
coating for ammunition with or without a combustible cartridge casing, 
which coating has sufficient heat-insulating and heat-absorption 
characteristics to prevent excessive local heating and to distribute 
external heat over a sufficiently large surface thereby providing 
protection against accidental ignition of the ammunition and/or the 
combustible cartridge casing due to local excessive external heating. 
It is a further object of the invention to provide a coating sufficiently 
delaying a possible ignition and having a composition leaving only a 
negligible residue after the firing of the projectile. 
It is an additional object of the present invention to provide a coating 
which protects sufficiently against moisture or soiling by oil or any 
deterioration due to fungi. 
It is a further object of the present invention that even under ignition 
inhibiting conditions such as for example malfunctioning of the smoke 
suctioning means or when the ammunition is soiled by oil or other material 
and/or is moist there will be a combustion of the cartridge without 
residue. 
It is an additional object of the present invention to avoid an 
uncontrolled ignition due to contacting with hot parts, such as, for 
example, after-glowing or after-flaming material in the loading chamber of 
the weapon, and/or hot or combustible oil drops or lighted cigarettes and 
to provide a resistant and preferably impermeable surface against the 
operation of water vapor, water, machine oil and fungi. 
These and other objects and advantages of the present invention will become 
evident from the description which follows. 
2. Brief Description of the Invention 
An improved ammunition of the present invention comprises a body of highly 
porous nitrocellulose permeated from the outside with a polymer carried by 
a solvent to form a binder for the body, an airy outer surface on the body 
of a layer of metal particles coated and connected with a polymer, and an 
outer coating of a rapidly cured resin on the airy outer surface layer of 
metal particles. 
A process is also provided for producing an improved ammunition with a 
surface coating having at least one layer of lacquer comprising preparing 
a highly porous nitrocellulose body, permeating the highly porous 
nitrocellulose body with a polymer carried by a solvent, substantially 
removing the solvent, covering the outer surface of the body with a 
dispersion of metal platelets in a second polymer solution with the second 
solution solvent permeating into the body for effecting a solid connection 
between the porous body and the metal platelets, and covering the 
resulting metal platelet surface layer with a rapidly curing resin 
dissolved in a third solvent, the third solvent carrying the second 
polymer in part from the metal platelet layer into the porous body and 
thereby creating hollow spaces or air pockets near the metal platelets. 
It has been found advantageous, for purposes of providing a complete 
protective effect, that is, a moisture-proof effect, resistance to oil and 
attack by fungi, and resistance to excessive exterior heating, to apply a 
first layer or coating in order to seal the pores of a combustible 
cartridge casing, respectively a body of powder mass, when dealing with 
ammunition having no cartridge casing, and thereafter to apply a second 
coating or layer consisting of a second polymer as a varnish or lacquer in 
which a metal powder is dispersed, and then applying as a final step a 
third coating consisting of an oil-moisture-and-fungi-resistant lacquer or 
varnish. Preferably there is added to the second polymer solution as a 
varnish or lacquer of the present invention 50-70 weight percent of metal 
powder, whereby the lower limit range is determined by the degree of 
decline in the ignition-inhibiting effect, whereas the upper limit of the 
range is determined by the decline in the adhesive capacity of the varnish 
or lacquer when it contains a high proportion of powder. When the metal 
powder consists of aluminum platelets their preferred concentration in the 
second polymer solution is from about 20 to 50 weight percent. 
It has been determined that a particularly favorable effect is obtained by 
the addition of metal powder if the particles in the powder have the form 
of small platelets. A particle size of the powder of between 10 and 100 
microns is effective. More preferred are powders having particle sizes 
from about 3 to 18 microns. The following metal powders have been found 
suitable and give particularly preferred results: aluminum powder, copper 
powder, zinc powder, as well as alloys, especially mixtures of these metal 
powders. Most preferred is aluminum powder in platelet form. 
It was determined that on the one hand the desired and required adequate 
protective effect was only achieved when the combined coatings had reached 
a certain minimum thickness. Surprisingly, it was also determined that the 
total thickness of the various coatings does not need to exceed a certain 
maximum value because, once this maximum thickness is exceeded, there is 
no further increase in the protective effect afforded by the coating or 
layer. The thickness of the total coating can be from about 0.05 to 0.1 
mm. A thickness of about 0.07 mm has proven to be an optimum value for the 
total thickness of the layers of the coating. This signifies that the 
necessary amount of coating substances, which are to be applied to the 
surface needs only to amount to about 80 g/m.sup.2, which, in comparison 
to the state of the art, is considered to be very favorable, because the 
quantitative consumption for the protective surface coating, according to 
the present invention can be considered quite small. Preferably, the 
resulting covered body is aired for at least about 10 days. 
In addition, such a thin coating layer avoids any type of difficulties 
regarding the ammunition tolerances and dimensions and the problems that 
may occur when such ammunition is inserted into a barrel of a certain 
caliber. 
In the production of the protective coating of the present invention, there 
can first be produced the ammunition itself having a combustible cartridge 
casing or such ammunition without a cartridge casing including the 
projectile, and then there is applied a gapless coating. Thus with the 
method of the present invention the projectile and the cartridge casing or 
the body of the powder mass forming the ammunition without a cartridge 
casing are not first applied separately with the protective coating layers 
and then assembled because, if the method were to be accomplished in this 
fashion, there would result a crack or interruption in the coating at the 
juncture of the individual assembled parts. Such crack or juncture would 
permit the penetration of moisture, oil, or fungi. Moreover, when 
separately coating the individual parts of the ammunition, it has been 
found that the coating thickness must be substantially thicker to provide 
an adequate protective surface coating and to have sufficient resistance 
to mechanical stresses. This is particularly so in view of the fact that 
the ammunition is subjected to further handling and operations before it 
reaches a finished state. 
The aforedescribed drawback is avoided with the present invention in view 
of the fact that the ammunition is immediately packed after the 
application of the coating layers and is not further handled prior to its 
actual use. For this reason it is not necessary to make the protective 
coating of the present invention particularly resistant to scratching. 
It has been determined during firing tests with ammunition having the 
protective surface coating in accordance with the present invention that 
the barrel erosion, when compared to that produced by conventional 
ammunition, is considerably reduced. While we do not wish to be bound by 
any theory, it is assumed that the protective surface coating during 
combustion of the cartridge casing or of the powder body forms a 
protective surface layer in the barrel which prevents or at least reduces 
the direct attack of the hot powder gases upon the inner surfaces of the 
barrel. 
In accordance with the present invention a coating for ammunition has been 
found wherein for example for a total weight of an ammunition charge of 
7700 g the weight of the coating amounts to at most about 20 g which is 
less than about 0.27 weight percent of the total weight. This coating and 
the easily combusted cartridge material are completely burned during 
firing without leaving any residue. Thus with the ammunition of the 
present invention the gun barrel receives improved characteristics for the 
sliding of projectiles therethrough. Erosion of the gun barrel is 
considerably reduced so that in lieu of the conventional 50 round firing 
capacity the gun barrels using the ammunition of the present invention can 
be fired up to tenfold of such conventional values; and this allows about 
500 rounds to be fired without an exchange of gun barrels. 
The invention accordingly consists in the features of construction, 
arrangement of parts and series of steps which will be exemplified in the 
process and article of manufacture hereinafter described and of which the 
scope of application will be indicated in the appended claims.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
In accordance with the present invention a body of highly porous 
nitrocellulose is prepared. The body can have the shape of a cartridge 
casing or that of any form useful in ammunition manufacture. In general, 
initially a pulp of nitrocellulose and reinforcing fibers is prepared. The 
reinforcing fibers are preferably derived from cellulose. They can be 
obtained as kraft cellulose by reducing wood chips in conventional fashion 
with an aqueous solution of sodium hydroxide and sodium sulfide under 
elevated temperature and pressure. After digesting, the reaction product 
is a fiber mass which is washed to free it from chemicals. Preferably the 
nitrocellulose contains at least about 13 weight percent of nitrogen and 
more preferably from about 13.2 to 13.4 weight percent nitrogen. The 
relative weight ratio of nitrocellulose to fibers can be preferably from 
about 1.8 to 2.5. The pulp can be formed as desired for the resulting 
ammunition. Additives can be incorporated in the ammunition body. Such 
additives include binders and stabilizers. The binders can be resins and 
are preferably two-component polyurethane resins. The amount of binder 
employed depends on the nature of the binder. A preferred amount of binder 
is from about 9 to 13 weight percent of the ammunition body. 
Preferably initially a raw form of nitrocellulose and fibers is formed from 
the pulp and pressed for obtaining a suitable wall thickness. Such wall 
thicknesses can be for example from about 3 to 4 mm. During the pressing, 
the residual moisture is preferably decreased to less than about 3 weight 
percent and ranges preferably below about 2 weight percent. After complete 
drying of the raw mold the body is preferably drenched with a solution of 
the resin. After evaporation of the solvent for the resin a highly porous 
body is obtained. The drying temperature is preferably from about 
80.degree. C. to 130.degree. C. The density of the nitrocellulose body is 
preferably from about 0.8 to 1 g/cm.sup.2. 
By drenching or soaking of the body with resin there is obtained a large 
gradient of resin concentration with higher values at the surface of the 
body and lower values at the inside of the body. As a result the 
nitrocellulose content near the surface is lower compared with the inside 
of the body. The surface of the body is thereby densified and even before 
applying any final protective coatings the surface already constitutes a 
protective layer against contamination and such protection is particularly 
effective against water. Such a surface also exhibits heat protective 
properties. 
Solvents for the applied resin for drenching the body depend on the resin. 
For example, solvents for polyurethane are generally free of water and do 
not have hydroxyl groups or other active groups. Solvents include polar 
and nonpolar organic solvents and solvent mixtures, which can comprise, 
for example, liquid aromatic hydrocarbons such as xylene and esters. A 
preferred solvent is zylene. The solvent should furthermore have a boiling 
point sufficiently low to provide for easy drying. This is necessary for 
removing the solvent substantially after permeating the highly porous 
nitrocellulose body with a polymer resin carried by the solvent. 
Employing polyurethane as a binder in accordance with the present invention 
results in a reticulation of the material of the body resulting in high 
strength and a lower transmission of the body compared with conventional 
cartridges such as those of U.S. Pat. No. 3,987,731. 
A stabilizer can also be incorporated in the ammunition body. The amount of 
stabilizer preferably is from about 0.4 weight percent to 1.5 weight 
percent of the total ammunition body. Suitable stabilizers include 
diphenylamine stabilizers. Preferably a stabilizer sold under the 
trademark Arkadite II is employed. 
The resulting body in general preferably comprises from about 55 to 65 
weight percent of nitrocellulose, from about 25 to 30 weight percent of 
cellulose fibers, from about 9 to 13 weight percent of a resin such as a 
two-component polyurethane resin and about from 0.4 to 1.5 weight percent 
of a stabilizer. One preferred composition of the body involves from about 
55 to 59 weight percent of guncotton, from about 29 to 33 weight percent 
of cellulose fibers, from about 9 to 13 weight percent of a polyurethane 
resin and from about 0.4 to 1.5 weight percent of a stabilizer. Another 
preferred composition of the improved ammunition of the present invention 
has a body of a composition of from about 59 to 63 weight percent of 
guncotton, from about 25 to 29 weight percent of cellulose fiber, from 
about 9 to 13 weight percent of a polyurethane resin and from about 0.4 
to 1.5 weight percent of a stabilizer. 
The finished ammunition body is first completely assembled and then the 
coating of the present invention is applied. This prevents a change in the 
ammunition after production of the coating of the present invention since 
possible permeable spots which can arise for example at the joint between 
the projectile point and the cartridge are sealed by the coating. 
The formation of the coating is preferably achieved by employing two 
coating steps not counting, however, a possible step of solvent dispersion 
on the surface for moving coating material in part into the body of 
nitrocellulose and fibers. 
The two step process is preferred in order to keep the coating weight and 
the coating thickness low for maintaining the combustibility of the 
ammunition body. In general, these requirements can only be achieved by 
employing at least two steps in the formation of the coating providing 
full protection for the ammunition body. For example, in an ammunition 
having a cartridge surface of about 1/4 m.sup.2 these requirements can be 
met by a coating weight of as low as 13 to 14 grams per cartridge. 
However, the coating weight can be increased up to the range of 18 to 20 
grams in this example. The first coating step covers the outer surface of 
the body with a dispersion of metal platelets in a second polymer solution 
with the second solution solvent permeating into the body for effecting a 
solid connection between the porous body and the metal platelets. The 
second polymer solution can be a solution as employed for example in the 
German published application No. 1 912 72. This treatment is effective to 
close and seal the pores of the combustible cartridge casing or the powder 
body itself. 
The following adhesive resins are suitable as polymers based on their good 
filler-absorbing characteristics, and they also have satisfactory heat 
resistance characteristics and also provide a good barrier action against 
water vapor and partially as well against water. Suitable resins include: 
1. physically dry resins: 
butyl rubber, also mixed with polyterpene resins, 
cyclized rubber (9 cyclo rubber), or 
novolaks, also mixed with polyvinylbutyrals, 
2. single component resins: 
urethane alkyd resins, 
alkyd resins mixed with polyvinyl butyrals or 
polyurethane resins. 
A preferred second polymer is cyclorubber. Cyclorubber has the approximate 
formula of (C.sub.5 H.sub.8).sub.x, which formula is about the same as 
that of natural rubber. Cyclorubber can be prepared from natural rubber in 
accordance with German patent DRP No. 675,564 issued July 7, 1936 and DRP 
No. 705,399 issued Sept. 15, 1939. A survey about cyclorubber is provided 
in the book by Hans Wagner and Hans Friedrich Sarx: "Kunstharzlacke", Carl 
Hanser Verlag, Munich 1971, pages 256-257. Cyclorubber in general has a 
melting point of about 130.degree. C. to 140.degree. C. and is dissolvable 
in most nonpolar solvents. Such solutions can be thinned down with most 
polar solvents. Preferred solvents include C.sub.7 -C.sub.15 hydrocarbons, 
turpentine, toluene, benzene, xylene, liquid aromatic hydrocarbons, 
tetrahydronaphthalene, decahydronaphthalene chlorinated hydrocarbons such 
as trichloroethylene and ketones such as cyclohexanone. More preferred as 
a solvent is xylene. Preferable cyclorubbers are those which are 
copolymerized for providing rapidly curable binders. Such copolymers 
include copolymers with styrene, methylstyrene or butylmethacrylate. Such 
a product is available from Reichold Albert Chemie AG. as Alpex CK 450. 
The afore-recited single component resins either harden oxidatively in the 
air or are crosslinked as a result of air humidity, even at room 
temperature, with sufficient speed. Even though no particular demands are 
made upon these coatings insofar as their resistance to oil is concerned, 
the satisfactory resistance of novolaks, urethane alkyd resins and 
polyurethane resins with respect to lubricating and hydraulic oils is 
considered to be an additional advantage. 
The second polymer solution has dispersed metal particles preferably in 
platelet form. Particle sizes between 10 and 100 microns are effective and 
preferred metal powders have particle sizes from about 3 to 18 microns. 
Suitable metal powders include aluminum powder, copper powder, zinc powder 
as well as alloys, especially from mixtures of these metals. Most 
preferred is aluminum powder in platelet form. The amount of metal, or in 
particular of aluminum, in the resin solution is limited by the required 
full wetting of all metal particles, which is necessary to achieve a 
sufficient adhesion of the metal layer on the body. The dispersion of 
metal platelets in the second polymer solution comprises from about 5 to 
10 weight percent of the second polymer. 
The thickness of the metal containing layer is preferably from about 0.04 
to 0.06 mm. The average density of the metal containing layer is 
preferably from about 0.95 to 1.08 g/cm.sup.2 in the case of aluminum in 
the final product. In applying the dispersion of metal platelets to the 
ammunition body the solvent penetrates into the nictrocellulose body and 
forms at the surface of the body a zone enriched in second polymer such as 
cyclorubber, which provides a solid bond between the metal particle layer 
and the ammunition body. 
The metal platelet surface layer is covered with a rapidly curing resin 
dissolved in a third solvent. The resulting covering layer of the surface 
coating consists of a cross-linked covering lacquer or varnish. With such 
a varnish or lacquer the best resistance to oils and water can be 
achieved. As raw materials for the lacquer or varnish serving as rapidly 
curing resin phenolic groups have been found to be suitable as building 
blocks for the lacquer system especially in the middle and higher number 
of phenolic groups. The hardening and curing of these varnishes and 
lacquers is effected: 
with phenolic resins by the addition of siccative; 
in the case of phenolic resins containing epoxides by the addition of 
"Versamides"; 
When using resols by the addition of special hardeners. 
("Versamide" is a registered trademark of Schering AG. of Berlin, 
West-Germany and covers a variety of polyamide type products.) 
In addition to the above-mentioned resin types, there can be also used for 
the covering layer the urethane-alkyd-resins or the polyurethane resins, 
which are preferred as heat-insulating layers. 
Preferred outer coatings include polyurethane resins. Such resins are 
obtainable by polymerization of isocyanates. For example an isocyanate can 
react with water to form an amine and the amine can start a polymerization 
by reacting with an isocyanate to form a substituted urea and the 
substituted urea can react with further urea to form a substituted 
carbamylurea, and so on. Preferred isocyanates are those which are not 
volatile and which exhibit low toxicity during application. Such 
isocyanates include the addition products of toluenediisocyanate with 
polyhydroxyl compounds; for example, three moles of toluenediisocyanate 
are reacted with one mole of trimethylolpropane to obtain a preferred 
isocyanate. 
A preferred polyurethane resin is distributed by Reichold Albert Chemie AG. 
as "Beckocoat PU 428". The polyurethane is generally applied in a 
solution. Solvents for the polyurethane are generally free of water and do 
not have hydroxyl or other active groups. Solvents include organic 
solvents and solvent mixtures which may comprise liquid aromatic 
hydrocarbons such as xylene and esters. Xylene is a preferred third 
solvent for the polyurethane employed as the rapidly curing resin. 
The third solvent dissolves part of the second polymer previously applied 
to the ammunition body and carries the second polymer further into the 
interior of the body and this transport of the solvent is enhanced by 
capillary activity. Thus an air-containing or airy metal layer reduced in 
resin content results. The polyurethane of the counter covering layer 
hardens in a very short time which is generally less than about ten 
minutes and does not penetrate the metal layer, since it is present in a 
prepolymerized form of a large molecular weight and therefore exhibits 
only limited flow capabilities. The thickness of the cured outer coating 
is preferably from about 0.015 to 0.03 mm. The total thickness of the 
coating of the body is preferably from about 0.05 to 0.1 mm. The formation 
of the airy metal layer increases especially the stability toward the 
effects of heat. 
Compared with conventional cover layers such as those disclosed for example 
in U.S. Pat. No. 3,987,731, according to the present invention the amount 
of aluminum can be considerably reduced. This assures a completely residue 
free combustion of the body with the protective coating. The process for 
obtaining the improved ammunition of the present invention can be 
controlled effectively by the solvent concentration. For example, when 
xylene is employed as the solvent, a higher concentration of xylene can 
increase the stability toward heat, since the xylene flows to the interior 
of the body. Furthermore, by increasing the amount of xylene the 
effectiveness against easy ignition can be increased. In addition, the 
body can be sprayed with additional solvent to increase the migration of 
the second polymer before applying the outer covering layer. 
The solvent of the outer cover layer is easily resorbed by the body in the 
course of the carrying process. For example cyclorubber is easily 
dissolved by the third solvent of the present invention and is transported 
toward the ammunition body. At the contact of the body with the metal 
layer this results in increased bonding. At the same time an airy metal 
layer with reduced resin content is formed. The congruence of the 
formation of the body with the adjustment of the process of applying the 
various layers is an important aspect of the present invention. 
Referring now to the drawing there is shown schematically the construction 
of the layers of the present invention and of the influence of the 
solvent, for example of xylene, on the achievement of such a product. The 
total body in this embodiment is a cartridge and is designated 1. The 
inner body is designated 3 and two outer zones are designated 2. The total 
layers are designated 4. The total layers comprise the metal layer 6 and 
the outer cover layer 5. The metal layer 6 is again separated in a zone 9 
of reduced resin content and in a layer 8 with increased resin content. 7 
designates in the layer of reduced resin content the aluminum layer 
construction as a porous air-containing aluminum structure. 
On the left side of the drawing there is indicated the effect of the 
solvent. In the outer region 13 there is an excess of solvent. By 
capillary action the solvent is transported into the outer cartridge zone 
10. The arrow between the numbers 11 and 12 indicates how the second resin 
such as cyclorubber is washed by the solvent into deeper layers resulting 
in an air pocket enriched porous aluminum structure. 
EXAMPLE 
The production of the cartridge is performed in the following way: First, 
pulp material consisting of nitrocellulose and kraft cellulose is 
prepared. From this pulp material there is formed a blank which is 
subjected to a pressing process so that it is converted into a solid sheet 
material having a wall thickness of about 3.3 mm and a residual moisture 
content of about 2 weight percent. After complete drying the formed 
material is soaked in a lacquer dissolved in xylene, the components of 
which are an isocyanate and a polyether mixture. The lacquer is formed 
with one part isocyanate for three parts polyether (respectively 
polyester) and four to five parts xylene. The xylene displaces during 
soaking the air in the dried formed body of the cartridge material. 
The lacquer now deposits between the fibers of the cartridge. The deposits 
occur preferably in the regions close to the surface of the body 
comparable to a chromatographic effect. After a soaking of about three to 
four minutes the drying is effected by evaporating the xylene and a 
lattice-like polymerization of the polyurethane is induced at a 
temperature of about 115.degree. C. for about 15 to 20 minutes. The 
soaking in polyurethane results in a large gradient from the surface down 
to the interior of the polyurethane concentration. 
The preferred material compositions of an impact round (KE) and of a 
multiple purpose round (MZ) are listed in the following table. The exact 
compositions for an impact projectile and a multiple purpose cartridge are 
as follows: 
______________________________________ 
Impact Multiple Purpose 
Projectile Cartridge 
weight percent 
weight percent 
______________________________________ 
Guncotton (13.2 to 13.4 
weight percent nitrogen) 
52.2 .+-. 1.5 60.7 .+-. 1.5 
Kraft cellulose 
31.0 .+-. 1.5 27.3 .+-. 1.5 
Two component poly- 
urethane resin 
11.0 .+-. 1.5 11.2 .+-. 1.5 
Arkadit II 0.8 .+-. 0.4 0.8 .+-. 0.4 
______________________________________ 
The prepared cartridge is finished and thereafter the coating is applied. 
Two layers are employed besides a soaking with xylene. This results in a 
low layer weight and in a low layer thickness. An ammunition body with a 
surface of about 1/4 m.sup.2 was covered with total layers having a weight 
of about 20 grams. The metal layer was provided by dispersion with a 
cyclorubber easily dissolvable in xylene. Aluminum platelets were 
dispersed in this solution. The xylene permeated the body surface and 
formed a zone enriched in cyclorubber at the surface of the body. 
The outer covering layer was provided by a polyurethane resin dissolved in 
xylene. The xylene in the outer covering layer dissolves the cyclorubber 
and drives it further into the ammunition body and the xylene transport is 
supported by capillary effects. A layer of aluminum platelets containing 
air pockets and a reduced content of resin results. The polyurethane 
hardens within about 10 minutes and does not penetrate into the aluminum 
layer. 
The following properties were observed with the product: 
The water permeability according to DIN 53123 was found to be 2 g/m.sup.2 
per day. The water absorption of a manufactured cartridge at 25.degree. C. 
and at a relative air humidity of 95% was found to be 2.5 g after four 
days and 10 g after 21 days. The residue after firing under unfavorable 
conditions was less than 0.1 per cartridge. Upon applying a lighted 
cigarette to the cartridge, upon the dropping of hot machine oil having a 
temperature of 250.degree. C. upon the cartridge, or dropping burning 
machine oil into the cartridge, no ignition was observed. 
Although the invention is illustrated and described with reference to a 
plurality of preferred embodiments thereof, it is to be understood that it 
is in no way limited by the disclosure of such a plurality of embodiments, 
but is capable of numerous modifications within the scope of the appended 
claims.