Note: Descriptions are shown in the official language in which they were submitted.
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A FIREARM INSERT FOR FIRING SMALLER CALIBRE AMMUNITION AND A
PROCESS FOR PRODUCING AN INSERTABLE BARREL
The present invention relates to an insert for a firearm, for
example, for a rifle sr a hand-held weapon, by means of ~hich
it is possible to fire ammunition of a smaller calibre than
that for which the particular firearm is designed. In
addition, a further object of the present invention is a
process by means of which it is possible to produce the
insertable barrel that is associated with this insert. Such
inserts are mainly used in large-calibre rifles or hand-held
weapons for purposes of training, so that the shooter can
practice firing and aiming at shorter ranges. In addition,
this s~all-calibre ammunition is less costly, and when it is
fired, it generates far less noise compared to the noise
lS generated by large-calibre ammunition. Thus, there is a great
demand for such inserts for firearms training. Firing small-
calibre ammunition is particularly well suited to training
novice shooters, for they can become accustomed to handling
large-calibre firearms and can gain experience in aiming and
delivering fire. Firearms training that is conducted by using
such inserts is less costly or, given the same costs, is more
efficient, for more ammunition can be fired. In addition,
firing that is conducted using ammunition of this calibre is
not governed by particular regulations so that it is not
always necessary to visit a rifle range; rather, such shooting
can be conducted in open terrain, for example, in a forest or
in open fields~ as well as in private property, when large-
calibre firearms can be used to fire such ammunition.
Typically, using 4 mm ammunition, which is commercially
available under the designation M20, shooting is carried out
at a range of 10 m.
Several versions of inserts of this kind that are used for
large-calibre firearms are found in the prior art. Towards
the end of the 1930s, the so-càlled Lienhard insert was
developed for the Swiss carbine, and this can also be fitted
to the Swiss Model S7 assault rifle, which is of the same
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calibre as the carbine. This Lienhard insert includes an
insertable barrel and a loading shell. The barrel insert
consists of a tube with an outside diameter that is the same
as the calibre of the rifle barrel, which is to say it has a
S diameter of 7.~ mm for this particular rifle. Two circular
grooves, spaced apart along the length of the insertable
barrel, are machined into its outer surface and a cord packing
or an o~ring of flexible rubber material is installed in each
of these. The insertable barrel has an i~side diameter that
amounts to at least 4 mm overall. Grooves that are 0.15 mm
deep are machined out of the inner side of the insertable
barrel, and these extend to the whole length of the barrel and
twist through one-quarter of a turn. ~he inside diameter
between two opposite grooves thus amounts to 4.3 mm, and to 4
mm between two opposing lands. A 4-mm caliber projectile that
i~ ~ired through the barrel, and which in point of fact has a
diameter of 4.3 mm, is pressed into the grooves and the spiral
path of th2 lands located between the grooves will then impart
a spin to the projectile, which stabilizes its trajectory.
When it is used, the ~ienhard insertable barrel is inserted
into the barrel of the particular rifle from the breech end.
Then the associated Lienhard loading shell is made ready.
Essentially, this consists of a hollow cylinder, the
projectile that is to be fired being installed at the front
end of this and a cap that is separated from the projectile is
installed on the rear end. When the weapon is fired, the
firing pin of the rifle bolt strikes the base of the cap and
the resulting explosion acts through the loading shell and
drives the projectile through the bore of the barrel. In
order to re load, the loading shell has to be removed from the
chamber, which is inconvenient, and the expended cap has to be
removed from it by using a pusher pin~ Then, the loading
shell has to be refitted with a projectile and a cap, and
inserted into the barr~l once again. For this reason, re-
loading requires time-consuming manipulation. A loading shell
that consists of two separable parts could also be used with
the Lienhard insert. At its front end, the foremost of these
accepted the projectile that was to be fired and behind this
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the charge which is separated from the projectile, the cap.
After the two parts had been assembled the rear part was
clamped to the base of the cap by means of a screw, so that a
blow on the rear end of the loading shell was transmitted
through the base of the cap, which caused the charge to
detonate.
The so-called Walter insertable barrel is an alternative to
this. Externally, this has the same shape as a GPll rifle
cartridge which can be fired both from the carbine and from
~he Nodel 57 assault rifle. It is 70 mm long and has a
continuous axial bore of 4 ~m diameter, within which helical
grooves are machined, with the result that the diameter
between two grooves amounts to 4.3 mm. Externally, this
insertable barrel which, in a way, is formed by the cartridge
itself, has two circular grooves in which flexible rubber 0-
rings are installed. The Walter insertable barrel is loaded
in that the ammunition is inserted into the rear end. The
ammunition thak is to be fired consists of a cartridge case
that is joined direckly to the projectile, which is of 4.3 mm
~iameter, and which is known by the designation M20. Several
such Walter insertable barrels can be stored in a magazine in
the same way as actual rifle cartridges. On loading, such an
insertable barrel is loaded in the chamber and the weapon is
fired when the firing pin of the rifle bolt which, in an
actual rifle cartridge strikes the base of the cartridge, now
strikes the base of the cartridge case of the M20 ammunition
that has be~n inserted. The projectile is then driven through
the bore o~ the barrel and discharged, when, once again, a
spin is imparted to it. The disadvantage o~ this insertable
barrel is the fact that it is held in the chamber of the rifle
only by means of the flexible rubber O-rings. Because of the
constant re-insPrtion, positioning becomes relatively
imprecise, and thus considerable dispersion of the shots is
unavoidable. Thus, accuracy leaves much to be desired. In
addition, if the trainee shooter does not wish to remove the
magazine after each shot~ in order to load the cartridges that
are combined with the insertable barrel, then he has to buy a
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number of such complete insertable barrels. Then, the can
prepare all of these and load them into the magazine, after
which he can fire the individual charges one after the other.
All that is needed is to complete a loading movement between
the individual shots. The procurement of a number ~f such
complete insertable barrels is, however, very costly.
Another solution for firing training ~sing large-calibre
rifles is offered by the ri~le insert that has become known as
the C02 insert, which was developed for short-range firing
with the new Swiss Model 90 assault rifle, which can be
procured commercially under the designation EP90. This rifle
insert consists of a breech piece into which a commercially
available C02 cartridge can be inserted, this being of the
1~ sort, for example, that is used to fill rechargeable soda-
water syphons. A projectile with a calibre of 5.5 mm is fired
using this rifle insert, and this equals the actual calibre of
this weapon. In point of fact, the projectiles may be of a
slightly larger diameter in order to take more of the
deviations that can result from continuous firing into
account. In order to fire the weapon with the C02 insert, a
projectile of this kind is loaded into the chamber of the
rifle, and this is then pressed forward into the bore by a
loading movement of the specially constructed breech piece, in
which a C02 cartridge has previously been inserted. The
breech piece incorporates a mechanism so that when the trigger
is operated, the valve of the ro2 cartridge is abruptly opened
and the pressure acts on the projectile that is accommodated
in the bore. A disadvantage of this insert is mainly that the
muzzle velocity of the projectile that can be achieved is too
low to achieve any great measure of accuracy. For this
reason, aiming must be carried out with a special addition to
the existing sighting system, which takes into account the
relatively low muzzle velocity of the projectile by imparting
a greater angle of elevation to the rifle.
Up to the present, there has been no insert that makes it
possible to fire M20 4-mm centre fire ammunition as training
20~32~4
ammunition for the Model ~0 assault ri~le, or the Model EP90
assault rifle, which have a calibre of 5.5 mm, and would
provide accuracy comparable to that achieved with the Lienhard
insert. This is attributable to the technical problem that it
is impossible to machine grooves into a bore of 4 mm inside
diameter and with an outside diameter of only 5.5 mm. ~he
barrel would be badly distorted or even destroyed by the
machining forces that are generated. It is true that an
insertable barrel of this kind can be produced in that one
first machines the grooves into a 4 mm bore with a larger
outside diameter, and subsequently turns the outside diameter
down to the desired dimension. However, such a process is
much too costly. First, six to twelve passes are required to
cut out grooves that are approximately 0.15 mm deep. In the
15 case of a barrel with the usual eight grooves, this results in
an extremely high number of machine passes that have to be
completed, which entails enormously high machining costs.
Second, the barrel becomes distorted and, for this reason, has
to be straightened subsequently. Third, its outside diameter
has to be turned down to the desired dimension. In order to
avoid high machining forces, it is only possible to remove an
extremely thin layer during each pass, for which reason, once
again, a large number of machining steps are required. An
insertable barrel produced in this way would become so costly
that there would hardly be any chance of selling it. In many
rifle barrels, very frequently the grooves are not machined
out but rather the barrel is cold formed around an appropriate
core. It is the opinion of the professional community that
this cold forming is impossible in the case of such small
diameters as a 4-mm insertable barrel for use in a firearm
with a calibre of 5.5 mm, because the material would split.
For the technical reasons set out above, up to now it has been
impossible to obtain an insert for the Model 90 assault rifle,
which includes an insertable barrel and which would actually
be insertable into the barrel of this rifle even though such
an insertable barrel would satisfy a very large demand. In
addition, there is no loading shell for M20 centre fire
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2~8328~
ammunition, which is the only effective type and which
requires a minimum of manipulation during re-loading.
For this reason, it is the task of the present invention to
S create an insert for firearms to fire reduced-calibre
ammunition using a weapon of larger calibre, in particular for
the Model 90 assault rifle or comparable weapons, which makes
it possible to achieve greater accuraGy and which requires the
simplest possible manipulation for re-loading. In addition,
0 it iS al80 a task of the present invention to describe a
procegs for manufacturing the associated insertable barrel.
The present invention solves this task by using an insert for
firearms, which are used to fire ammunition of smaller calibre
than that for which the particular weapon is designed, with an
insertable barrel and a loading shell that is of two separable
parts, and which is characterized in that at an inside
diameter of the insertable barrel of less than 5 mm, the ratio
of the dimension of its insîde to its outside diameter is more
than 60%; and in that a one-piece munition consisting of a
cartridge case and a projectile can be inserted into the
foremost part of the loading shell, a firing pin being so
supported in its rearmost part so as to be moveable in an
axial direction.
In addition, the present invention solves this problem by
means of a process for manufacturing an insertable barrel for
this insert that is characterized in that the grooves and the
lands in the bore are produced in the barrel by means of cold
forging from the inner side of the tube of a greater outside
and inside diameter than the barrel that is to be produced, in
that a plurality of hammers that are arranged peripherally
around the tube act radially and simultaneously on its outside
diameter and against its stationary core, which is located
within it and which has the negative shape of the appropriate
grooves and lands, the tube being drawn off the core beneath
the hammers whilst being appropriately rotated, after which
the outside is turned down and fine finished.
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~ The insert according to the present invention makes it
; possible to fire ammunition of a reduced calibre using
firear~s that are designed for larger calibre ammunition. ~he
S loading shell of the insert according to the present inYention
can be loaded into the conventional magazine of the firearm
and ~anipulated in exactly the same way as the ammunition for
which the weapon is designed. In particular, a magazine that
has been filled can be emptied shot by shot when all that is
required betwee~ the shots is a manual loading movement. When
this i~ done, the loading shell is automatically ejected, in
exactly the same way as a spent rifle cartridge case. The
particular production process for the associated insertable
barrel permits production that is so cost-effective that, for
the first time, an insertable barrel that can actually be
inserted into the rifle barrel can be offered for sale.
Furthermore, the insertable barrel according to the present
invention is of such superior precision that the effectiveness
of firing training with surh small-calibre ammunition can be
very grea~ly increased. Tests have shown that the dispersion
pattern achieved at a range of 20 m is sufficient to render it
effective to practice at this range.
An embodiment of the invention is shown in the drawings
appended hereto and described in the followiny description
with reference to the drawings. These drawings shown the
following:
Figure 1: the front part of the loading shell in
longitudinal cross part, with ammunition inserted
in it, and to the right of this a view of the same
loading shell part from behind;
Figure 2: the rear part of the loading shell with the firing
pin, in longitudinal cross section, and to the
right of this a view of this part of the loading
shell from the front;
Figure 3: the loading shell with the ammunition prior to
assembly, in a perspective view;
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Figure 4: the assembled loading shell when loaded at th~
moment of firing, in longitudinal cross section,
and beneath this a conventional rifle cartridge
for purposes of comparison; Figure 5: the insertable barrel in longitudinal cross
section with the loading shell adjacent to it;
Figures 6a to 6d: the process for producing the insertable
barrel at three point~ of the~process, and the
finished insartable barrel, each in longitudinal section.
The insert according to the present invention consists of a
specially developed loadin~ shell and of an insertable barrel
produced by a unique, specially developed process. These two
elements of the insert are matched to each other and together
for~ the underlying con~ept of the present invention, in that
they work in conjunction with each other. Figure 1 is a
longitudinal cross section through the front part 1 of the
loading shell that ~orms part of the insert and this,
according to the present invention, is configured in two
parts. This front p~rt 1 of the loading shell is essentially
a hollow cylinder that forms a female part for the rear part
~f the loading shell~ Its outside diameter matches to a large
extent that o~ a conventional rifle cartridge in its front
axea, so that this front part 1 of the loading shell fits into
the appropriate cartridge chamber of the firearm. The inner
side consists of sections of di~ferent diameters. In the
rearmost area 2, the inside diameter is greatest, and this is
then followed by an area 3 of a somewhat smaller inside
diameter; finally there is another area 4 with an inside
diameter that is even smaller~ Ad3acent to this, in the area
of the foremost opening, there is a funnel-shaped tapered
section 5 that finally makes a transmission to become the
actual opening 6 with the smallest inside diameter. The
ammunition 7 that is to be fired fits into this funnel-shaped
area 5, 6 of the opening area of the front part 1 of the
loading shell, and this ammunition then protxudes somewhat
from the front of the loading shell itself. The ammunition 7
can be inserted there in that it is pushed into the front part
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:
1 of the loading shell from behind and is then held by a
positive shape fit in the opening area 5, 6, as is shown in
figure 1. In practice, when it is loaded, the front part 1 of
the loading shell is held vertical so that the largest inside
S diameter is on top, whereupon the ammunition 7 can be dropped
into this foremost part ~ of the loading shell. The right-
hand drawing in figure 1 shows the front part of the loading
shell as viewed fxom the rear. Viewed together with the
longitudinal section, it can be seen that the area 3 that ha~
the ~econd largest diameter has two opposing areas of smaller
diameter 8 at the rear; these extend through approximately 90
of the periphery and are opposite each other. This means that
the recesses 9 are formed, as can be seen in the view from
behind. These recesses 9 or the areas 8 of smaller diameter
are part of a bayonet catch, as will be explained below.
Figure 2 shows the male part 10 that can be inserted into the
female part 1 that is shown in figure 1, which has just been
described. This male or rear part 10 of the loading shell
according to the present invention also forms a hollow
cylinder with which a firing pin 11 is supported and guided in
an axial direction, and which has an appropriately small
diameter. This firing pin 11 is additionally guided at the
rear by means of a guide sleeve 12 which also prevents it from
falling out of the loading shell. It has a thickened section
13 in its middle area, and this is somewhat shorter than the
corresponding recess 14 in the inside wall of the hollow
cylinder, so that the thickened portion 13 is guided in this
recess 14, al$hough the firing pin 11 can be moved through a
specific range of movement in an axial direction. The firing
pin 11 is of an equal length to the total rear part lo of the
loading shell. At the front, this firing pin has a rounded
tip 15 that is intended to strike the base of the cap of the
ammunition. Externally, the rear part 16 of the male loading
3s shell part 10 is shaped so as to be identical of the shape of
a conventional rifle cartridge. Thus, it has a projecting rim
15 that is created by appropriate recesses 18 and which is
intended to work as a stop for the ejector on the bolt of the
2~3~8~
weapon. The front part 19 of the male loading shell part 10
has outside diameters that are the same as the associated
inside diameters of the female front part l of the loading
shell shown in figure 1. In particular, it has two thickened
S sections ~0 that similarly extend for approximately 90 around
the periphery and when rotated appropriately with respect to
the front part 1 of the loading shell these correspond to the
recesses 9 in this. To the right of ~he longitudinal section
that is shown in figure 2 there is a front view of the male
loading shell part 10, in which these two thickened areas 20
can ~e seen.
Figure 3 is a perspective view of the loading shell 21 with
the ammunition 7 that is to be inserted into it, this showing
the loading shell before assembly. This drawing shows the
female front part 1 and the male rear part 10 of the loading
shell 21. In the area l9 of the rear part 10 there are the two
sections with different diameters, and the thicker areas 20
which form part of the bayonet catch. At the rear end of the
rear part 10 of the loading shell 21 there is the rim 17 that
is required to eject the loading shell 21 after the ammunition
has been fired. Between the two parts 1, 10 of the loading
shell 21 there is the ammunition 7, as it is to be inserted
into the front part 1 of the loading shell 21. This consists
of a cartridge case 22 and a 4~mm projectile 23 that is
installed on the front end of the cartridge case 22. After
the loading shell 21 has been assembled, the projectile 23 and
the front edge of the cartridge case 22 extend from the
drilling in the front part of the loading shell 21.
Pigure 4 shows the two parts 1, 10 of the loading
shell 21 as assembled just prior to firing. The male rear
part 10 of the loading shell 21 is inserted into the female
front part 1 after the ammunition has been installed. To this
end, the two parts l, 10 have to be rotated relative to each
other so that the thickened portions 20 on the rear part 10
enter the recesses 9 in the front part 1. It is only when in
this rotated position that the two parts 1, 10 can be inserted
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2~28~
one into the other. After this, they are secured against
coming apart by being rotated, when the thickened parts 20 on
the rear part 10 rotate over the corresponding narrow sections
8 on the front part 1 in the manner of a bayonet catch when
S they come to a solid stop on this. Because of a slight slope
to the surfaces of the thickened parts 20 that lie against
each other, or similar slope on the narrower portions 8 on the
two parts 1, 10 the rotation of the parts 1, 10 relative to
each other results in increasing friction, which then prevents
the parts 1, 10 from rotating and being loosened. In this
position, when they are inserted into each other, the front
end of the male loading shell part 1 presses the ammunition 7
into ths funnel-shaped recess 5, 6 in the area of the opening
of the front loading shell part 1. Of course, other means
~5 could be used to connect the two parts 1, 10. For example, it
would also be possible to use a threaded connection, so that
the t~o parts could be screwed together. If the loading shell
that has been assembled and loaded in this manner is now
inserted into the weapon, and if the trigger of the weapon is
operated, the firing pin of the rifle bolt strikes the firing
pin 11 inside the loading shell 21, and the tip 15 of this
then, in its turn, strikes the base of the ammunition 7 and
causes the charge within it to explode. The loaded and
prepared loading shell 21 that is shown in figure 4 can be
handled in exactly the same way as a conventional rifle
cartridge. For purposes of comparison, a conventional rifle
cartridge 25 is shown beneath the drawing of the loading shell
21 in its assembled state, and it can be seen that the
dimensions of this cartridge 25 are identical to those of the
loading shell 21 up to and including the projectile 26 that
extends from the front of the loading shell. Thus, a
plurality of loading shells 21 that have been prepared in this
way can be loaded into the magazine of the weapon and a
loading movement of the rifle bolt will expel this loading
shell 21 in exactly the same way as the spent casing of a
conventional rifle cartridge, even if the loading movement of
the bolt has not been initiated by the pressure generated by
2~3~8~
the explosion of the ammunition that is fired, but rather by
manual operation.
Up to now, only the loading shell 21 of the insert has bsen
S described. Using thi~ loading shell 21, it is possible to
fire ammunition of a calibre that is smaller than that for
which the rifle barrel has been designed. The second element
o~ the insert according to the present invention is thus an
insertable barrel that can be inserted into the existing
barrel of the ~irearm, thereby reducing the inside diameter or
calibre of this. What is particularly difficult in respect to
the insertable barrel for the Model ~0 assault rifle is the
fact that the calibre of this rifle is not much greater than
that of the small-calibre ammunition that is to be fired. Its
~5 calibre is 5.5 ~m, whereas the smaller-calibre ammunition that
is to be fired, which is designated M20 centre fire
ammunition, has a diameter of 4 mm. The wall thickness of an
insertable barrel that is suitable for this purpose and which
is intended ~or insertion into the conventional barrel of the
Model 90 assault rifle, as is designated EP90, is thus
unavoidably extremely thin.
Figure 5 is a longitudinal cross section through an insertable
barrel 27 of this kind, and it also shows the associated
loading shell 21 with the ammunition 7. In order to fire M20
centre fire ammunition, this insertable barrel has an inside
diameter of 4 mm measured across the grooves, whereas the
inside diameter measured across the lands is 4.3 mm. For this
reason, the ratio of the dimension of the inner to the outer
diameter of the insertable barrel 26 amounts to more than 60%,
in comparison to that of the Lienhard insertable barrel, in
which this ratio is clearly under 60~ for the same ammunition.
The grooves 2~ and the lands 29, which twist through 90 along
the length of the barrel, are shown on the inner side of the
insertable barrel. At the breech end 30, the insertable
barrel 27 has a small thicker area 31 and the end edge 32 is
funnel-shaped on the outside. The projectile 23 of the
ammunition 7 is located at the funnel-shaped opening 5 of the
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2~32~
insertable barrel 27 when the weapon is loaded, as can be seen
from figure 5. The remaining outer side 33 of the insertable
barrel 26, which is adjacent to the thickened section 31, is
machined so as to be smooth along its whole length and thus
S ha~ neither raised nor depressed sections.
It is a particular technical problem to create the required
grooves 28 and lands 29 in such a thi~-walled insertable
barrel 27, such that production costs can be kept within
10 acceptable limits. It is impossible to machine out the
individual grooves 28 with subsequent honing and lapping of
the barrel because of the high production costs discussed
above. The costs that are associated with this would be
unacceptable. In addition, every barrel would have to be
lS subsequently straightened because the reaction forces of such
processing would unavoidably twist it. In view of this
problem, the pre~ent invention has created a process which
treads a completely new path for such small bore diameters,
in that the grooves 28 and the lands 29 are formed on the
inside of the bore by means of cold forming of the barrel 27
about an appropriately-shaped core that is at least as long as
the length of the barrel. Grooves 28 and lands 29 are already
~orged in rifle barrels by cold ~orming about a core.
However, the cores that are used to do this are only a few
centimetres lon~, and never as long as the rifle barrel
itself. During the shaping process they are held under
tension on the core by a tapered extension which extends to
the whole length of the barrel whilst the barrel is drawn off
the core, under the hammers that are used in the shaping
process. After ~orming, the barrels are straightened since
they are unavoidably bent during the forming process. The
smaller the barrel diameters, the more the distortion that has
to be expected. In addition, straightening would be too
costly for small insertable barrels. Expert opinion is that
the production o~ an insertable barrel with a diameter that is
clearly much smaller is impossible using the known process for
cold forming, for this would unavoidably destroy the thin-wall
materialO In contrast to this, the present invention creates
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a process for producing grooves 28 and lands 29 in an
insertable barrel 27 having such a small inside diameter, by
means of cold forming, in that the barrel is hammered over a
core that matches the negative shape of the desired inside of
S the barrel and which extends to the whole length of the
barrel. A core that is configured in this way, and i8 of high
speed steel, will always provide the barrel with the required
stability when it is being ~haped by ~he hammers, so that no
distortion takes place and it thus becomes unnecessary to
straighten the barrels subsequently. Three different stages
in the process according to the present invention are ~hown in
figures 6a to 6c, and ~igure 6d shows the finished insertable
barrel. For purposes of clarity, the insertable barrels in
figures 6a to 6d are all shown in one cross section. For an
lS insertable barrel that is 110 mm long, for example, and which
is intended for insertion into the Swiss Model 90 assault
rifle, a standard tube 34 with an outside diameter of 11 mm
and an inside diameter of 5 mm is used. This tube 34, which,
for purposes of forming, should advantageously have a length
of at least approximately 180 mm, is installed over a core 35
of high-speed steel that is approximately 150 mm long. From
one end 36, the outside of this core 35 corresponds to the
negative form of eight grooves 28 and eight lands 29 to a
length of at least llO mm, and these make one-quarter turn
along this length of 110 mm.
Figure 6a shows the situation at the beginning of the cold
forming process. The standard tube 34 is installed completely
over that part of the core 35 that has the grooves 28 and the
lands 29. The unattached end 37 is clamped into a shaping
machine, by means of which it can be withdrawn in an axial
direction whilst the core 35 is ~eing rotated. The core 35,
in its turn, is clamped firmly by its unattached end 38. The
hammers 39 work in the same stationary location with reference
to the core 35. At the start of the process, as is shown in
figure 6a, the hammers 39 strike the outer side of one end of
what is to be the insertable barrel. It is advantageous that
the eight hammers 39 strike simultaneously, these eight
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2~3~8~
hammers 39 being arranged equidistantly about the periphery sf
the standard tube 34, and each strikes the outer surface in a
radial direction. Every pair of hammers 39 is opposite each
other, 80 that the striking forces that they generate act
opposite to each other and ~hereby cancel each other out. It
is advantageous that the hammers 39 have striking surfaces
that are curved concavely so as to be an approximate match to
the outsid~ surface of the tube. Duri~g the ha~mering process,
the tube is now drawn slowly off the core 35 and at the same
time a rotational movement is superimposed on this axial
movement, this corresponding to the turns of the grooves 28
~nd the lands 29 with reference to their negative shape on the
coxe 35. Shortly after this, the situation is as depicted in
figure 6b, in which the tube 34 has been withdrawn from
1~ approximately half the core length, so that about half of what
is to be the barrel has already been formed. The forming can
be seen by the taper of the tube 34 in the area 27 that has
already been processed. This processing is continued until
finally the tube 34 is drawn off the core 35, as is shown in
figure 6c. Given the dimensions that are shown in this
example, the outside diameter of the tube 34 is tapered by
approximately 2 mm by the hammer blows, this resulting in a
new outside diameter of approximately 9 mm. However, the
outside diameter of the insertable barrel 27 must be so small
that the insertable barrel 27 fits into the rifle barrel. In
the case of the Model 90 assault rifle, the internal diameter
is 5.5 mm measured over the lands. However, this diameter
becomes somewhat larger, i.e., at the mid-point by about 3 to
6/lOOths mm, once a certain number of shots have passed
through the barrel. The outside diameter of the insertable
barxel 27 is now finished to this final dimension, in that it
is first turned down to an outside diameter of 5.7 mm. A
thickened area, of which the edge 32 is funnel-shaped on the
outside, is left in place right at the bolt end. Finally, the
outside diameter is fine-machined to a dimension of 5.56 mm,
after which the insertable barrel 27 is cut to the desired
length, in the exampl~ shown to 110 mm, so that it ultimately
appears as shown in figure 6d. The finished insertable barrel
2~28l~
is shown in longitudinal section in figure 6d. The accuracy of
an insertable barrel 27 that is produced in this way is so
- high that the tolerance of the inside diameter to its length
of 110 ~m does not exceed l/lOOth mm in the present example.
S The hots that are fired from it are correspondingly accurate.
In order to determine the dispersal accuracy of a rifle, it is
first clamped into position and 10 shots are fired from it.
The total of the points scored is a metric for the precision
of the particular rifle. Rifles ~hich, when fired at a range
of 300 m at an A-type target, with 10 rings, achieve a point
score of 96 with 10 such ~hots are considered as first-rate
firearms in knowledgeable circles, and can be offered for sale
as such. Firing is conducted at 10 m using the
correspondingly smaller target with 10 divisions, as used for
small-calibre weapons. Tests have shown that a Model 90
assault rifle fitted with the insert according to the present
invention, and firing M20 centre fire ammunition at a 70 m
range can achieve a 100 shot image, which is to say a total
point score of 100 when fired at a No. 10 disk (as a dispersal
pattern). Becau~e of its outstanding precision, the insert
according to the present invention is best suited for small-
arms training. Firing as well as aiming can be practised very
economically, at a level of effectiveness that has been
unachievable up to now. The rifle can be converted very
simply by installing the insertable barrel 27 in the breech
end opening of the barrel. After firing ammunition of a
smaller calibre using the insert according to the present
invention the rifle can be reconverted for normal operation in
that the insertable barrel 27 is pushed out of the barrel
using a plastic rod which is inserted into the barrel from the
muzzle end. It is, of course, understood that the insert
according to the present invention can be produced for a large
number of rifles or even pistols and revolvers by using the
appropriate dimensions. The only condition is that the outside
diameter of the associated insertable barrel be matched to the
calibre of the rifle or hand-held weapon that is to be used
and the loading shell correspond to a normal rifle cartridge
for the particular firearm, in relation to its external
- 16 -
2~3~8'~
dimensions. For this reason, and in particular, it is
possible to produce an insert for the Swiss Model 57 assault
rifle and the Swiss carbine. Then, the insertable barrel will
have an outside diameter of 7.55 mm and the exterior of the
S associated two-part loading shell will correspond to the rifle
cartridge 11 that is usually fired from this weapon.
- 17 -
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