Belt-advance mechanism for an automatic gas-loading belt-feed weapon, especially a machine gun

A belt-advance system for a belt-fed gas-loading automatic weapon, e.g. a machine gun, revises the usual energy flow path by obtaining at its input side a gas-pressure pulse upon the firing of the weapon and providing an energy-storage unit functionally combined with a cylinder/gas-piston unit for transforming the pneumatic energy into mechanical energy for stepping the belt-advance ratchet pawl.

FIELD OF THE INVENTION 
The present invention relates to automatic weapons, such as machine guns 
and machine cannons, which are belt-fed and, more particularly, to a 
belt-advance mechanism for such a weapon. 
BACKGROUND OF THE INVENTION 
Modern automatic weapons over the full caliber range make use of a variety 
of mechanisms for feeding the cartridges into the breech of the weapon. 
Mention may be made, in this connection, of magazine feeders, turret 
feeders and belt feeders. Of concern to the present invention, however, 
are belt-feeding mechanisms for such automatic weapons. 
In addition, mention may be made of the various ways in which the belt can 
be advanced, e.g. by the use of recoil energy or by gas power. It is an 
advancing system of the latter type with which the present invention is 
concerned. 
In gas-powered belt-advancing mechanisms for belt-fed automatic weapons, 
such as machine guns, an energy-flow path can be provided which at its 
input side, is formed by a gas passage for tapping the high pressure of 
the gas propellant which drives the bullet or projectile from the barrel 
of the weapon upon the firing thereof. 
The gas passage feeds a cylinder/gas-piston unit which converts the energy 
of the propellant gas (pneumatic energy) into mechanism energy, the output 
of the gas piston being applied to a ratchet pawl and a transport shaft 
for stepping the belt and aligning the next cartridge thereof with the 
breech or cartridge chamber. 
A time-delay unit is provided in this energy-flow train in the form of a 
mechanical energy storage device, e.g. which can have springs compressible 
by the pneumatic energy. 
The belts which are used in such automatic weapons generally are formed as 
a flexible element or with a plurality of articulated links and have 
spaced apart seats, e.g. in the form of clips, into which the respective 
cartridges can be pressed. 
The gas-pressure loading utilizes the highly compressed propellant gas 
behind the projectile and branches a small fraction of the volume of this 
propellant gas from the barrel behind the projectile upon the firing 
thereof and before the projectile has fully escaped from the barrel of the 
weapon. 
When such compressed gas is used to actuate accessories of the weapon, e.g. 
the cartridge-feed ratchet pawl and the belt-displacement shaft, care must 
be taken to bear in mind the mass of the belt and hence its inertia. 
The problem is that the gas pressure pulse is only applied for a brief 
instant during each firing cycle. 
Because of its inertia or mass of the belt, the latter responds to forces 
tending to advance the belt, especially if they are practically 
instantaneous by a retardation which applies considerable stress to the 
belt. These stresses may cause tearing of the belt. 
In German Pat. No. 1,290,455 there is described a system which is intended 
to avoid this disadvantage. In this system, the gas pressure upon firing 
of the weapon is recovered as pneumatic energy and the pneumatic energy 
is, in turn, transformed into mechanical energy in a cylinder/gas-piston 
unit. The gas piston actuates in its working stroke a ratchet pawl which 
is provided with a restoring spring and the ratchet, in turn, stresses a 
plurality of spirally coiled, prestressed band-type coil springs which 
collectively form a stack serving as a force-storage device. 
After the stored energy reaches a certain level, it is applied to a 
belt-feed mechanism, for example via a shaft. 
This system has the advantage, because of the conversion of the gas 
pressure into mechanical energy which is stored, that the stored 
mechanical energy can effect the advance of the loading belt in a highly 
reproducible and reliable manner because mechanical energy can be 
recovered from storage over a fixed path and for a fixed interval fully 
reproducibly over many operating cycles. However, it has the disadvantage 
that the time required for stressing the energy-storage spring and 
recovering the energy from the mechanical storage is considerable and, if 
reduced or eliminated, could enable the advance of the belt more rapidly, 
i.e. allow the transmission of energy along the path from the rise of the 
pneumatic pressure (i.e. the generation of the energy pulse) to the 
actuations of the advancing mechanism for the belt to be shortened. 
This is particularly important for automatic weapons which are to have a 
high fire power and hence a more rapid loading cadence and rounds per 
minute firing capability than lower fire-power weapons. 
In addition, the increased length of the energy transmission train of 
necessity involves a number of mechanical components which increase the 
fabrication cost of the weapon, the maintenance operation required for it 
and the complexity with concomitant danger of decreased reliability. 
Another disadvantage of the longer energy train is, of course, the 
increased size and weight of the weapon. 
In practice, it has been found that the storage spring systems of the 
earlier weapons require frequent checking to avoid malfunctioning due to 
settling. 
Finally, a disadvantage of the earlier systems is a need for a large number 
of parts which tend to wear and must be replaced so that logistical 
problems can arise in the use of such weapons. 
OBJECTS OF THE INVENTION 
It is the principal object of the present invention to provide an improved 
belt-advance system for a belt-feed gas-loading automatic weapon whereby 
the aforedescribed disadvantages are avoided. 
Another object of the invention is to reduce the length and complexity of 
the energy-flow train in a belt-advance system for a belt-feed gas-loading 
automatic weapon such as a machine gun or machine cannon. 
Still another object of the invention is to provide an automatic weapon 
with improved fire power and hence loading cadence which has a reduced 
number of parts, by comparison with earlier systems, is more reliable, is 
less expensive, requires less maintenance and is less bulky. 
It is also an object of the present invention to provide a belt-feed drive 
of the aforedescribed type which is more rapidly operating and of lower 
cost while being free from the disadvantages of the earlier systems. 
SUMMARY OF THE INVENTION 
These objects are attained, in accordance with the present invention, in a 
belt-advance system for an automatic belt-feed gas-loading gun, especially 
an automatic weapon such as a machine gun or a machine cannon, which is 
provided with an energy-flow path initiated at a passage communicating 
with the barrel of the weapon for receiving pneumatic energy in the form 
of a high pressure propulsion-gas pulse upon the firming of a round in the 
chamber of the weapon. The energy-flow path includes a cylinder/gas-piston 
unit for transforming the pneumatic energy of the propellant gas into 
mechanical energy and a ratchet mechanism connected to the belt-advance 
wheels or the like and whose member is restored to its initial position by 
a spring but which is activated by the mechanical energy to step the belt 
and bring the next round to be fired into alignment with the chamber. 
According to the present invention, the energy storage device is 
constructed and arranged so as to store the gas or pneumatic energy 
(rather than the mechanical energy after transformation as in prior art 
systems) and is provided, in the energy-flow direction, ahead of the 
cylinder/gas-piston unit while being functionally integrated therewith. 
The major advance resulting from the modification of the energy-flow path 
of the prior art, in accordance with the instant invention, is the 
significant simplification of this energy-flow path with the drastic 
reduction in the number of moving parts and elements of the belt-advance 
mechanism or system and the significant reduction in the mass which must 
be displaced to step the munitions belt. 
According to a feature of the invention, the gas-energy storage device is 
integrated with the cylinder/gas-piston unit in space as well as 
functionally, i.e. both can be provided in a common housing or mounting. 
It has also been found to be advantageous to maintain a connection between 
the belt-advance mechanism and the stepping ratchet during the entire 
working stroke of the latter. 
It also has been found to be advantageous, moreover, to provide the 
energy-storage unit which includes a gas-storage chamber or reservoir 
which is provided with an inlet of defined flow cross section and volume 
such that a jump in the pressure p.sub.v ahead of the inlet over 
atmospheric pressure, a ratio a=p.sub.v /p.sub.h is obtained which very 
rapidly becomes unity while with rapid fall of p.sub.v against the 
atmospheric pressure, the reciprocal ratio 1/a falls comparatively slowly 
to unity, p.sub.h representing the instantaneous pressure downstream of 
the inlet. 
Advantageously, the flow cross section at the inlet upon a forward pressure 
differential across the inlet is greater than the flow cross section with 
the reverse pressure differential, i.e. a gradient in which the pressure 
behind the inlet is greater than that ahead of the inlet. 
A bypass with fixed flow cross section can be provided to achieve the flow 
conditions mentioned above and can be provided in conjunction with a valve 
body which is shiftable into its open position by a pressure differential 
with the higher pressure in the upstream side of the inlet can be formed 
in the tap at which the gas pressure is supplied from the barrel of the 
weapon to the gas passage leading therefrom. In this case, of course, the 
volume of the gas passage is included in the volume of the gas storage 
compartment. 
We have found it to be advantageous, moreover, to provide means for 
adjusting the capcity (volume) of the energy-storage compartment and for 
varying the effective volume of the energy-storage system as a whole. 
The feeders of the invention discussed above permit considerable 
simplification of the belt-advance system for the automatic weapon.

SPECIFIC DESCRIPTION 
We have shown in FIG. 1 a state-of-the art energy-flow train in the most 
diagrammatic form, for the stepping of the munitions belt of an automatic 
weapon. 
As illustrated in the aforementioned German patent, the weapon belt may be 
provided with clips in which respective rounds or cartridges are seated, 
the belt being passed over a sprocket wheel or the like which is stepped 
by the ratchet mechanicm for advancing the rounds one by one into 
alignment with the firing chamber of the weapon. For details with respect 
to the belt, the firing mechanism chamber and guide means for munitions 
belt, reference may be had to the aforementioned patent, the references 
cited therein and other art in the same international patent 
classification class and subclass. The details of the ratchet likewise are 
not a part of the invention and the ratchet may be the stepping pawl or 
lever used in the aforementioned patent. 
However, FIG. 1 does show that the energy train commences at the barrel or 
firing chamber 1 behind the projectile which is to be propelled, upon 
firing from the barrel by ignition of the charge of the cartridge and the 
generation by such ignition, of the propellant gases. The gas pressure 
from behind the projectile is tapped at 6 and is fed by a gas passage 7 to 
the input side or port 8 of a cylinder/gas-piston unit 2, the gas piston 
of which has not been illustrated in FIG. 1. The output 9 of the gas 
piston is effective upon the stepping ratchet 3 which is coupled with the 
input 10 of an energy-storage device 4 which, as described for the prior 
art previously, can be constituted by a stack or set of springs, the 
restoring movement of the ratchet level 3 being effected by a spring as 
well. 
The energy-storage device 4 effectively has an output 11 which is coupled 
with input 12 of a transport device 5, e.g. an advancing shaft. 
Upon firing of a round from the chamber, the propellant gases generate 
pressure behind the projectile and part of the volume of the propellant 
gas in a highly energetic form is branched through the passage 7 to the 
input side 8. This branched gas-pressure energy can be represented by 
E.sub.g and is thus applied to one side of the gas piston to initiate a 
predetermined working stroke thereof. 
The gas-pressure energy is transformed thereby into mechanical energy 
E.sub.m. 
Because the gas pressure rise time within the chamber, upon firing, is only 
of the order of milliseconds, the gas pressure energy E.sub.g is only 
available for a corresponding time period and is applied in a pulse to the 
gas piston. 
This pulse actuates the ratchet pawl 30 against the restoring spring 
thereof and transfers the mechanical energy E.sub.m to the input 10 of the 
force-storing spring system 4 to transform its mechanical (kinetic) energy 
E.sub.m to mechanical energy (potential+kinetic) E.sub.m ' which appears 
at the output 11 of the energy-storage device 4 and is applied to the 
input 12 of the transport device 5. 
The energy-storage device 4 thus functions as a delay device which, because 
it is mechanically coupled to the ratchet pawl 3, permits the brief energy 
E.sub.g to be applied over a longer period as the mechanical energy 
E.sub.m '. Devices of this type are very complex and expensive as has been 
noted below. 
The energy-flow train according to the invention has been shown in FIG. 2 
in the same form as FIG. 1. It can be seen from this Figure that the 
energy-storage unit 4' is not located behind the ratchet pawl 3, but 
rather is integrated with cylinder/gas-piston unit 2 and is provided ahead 
of the ratchet pawl 3 so that the gas-piston unit itself is displaced over 
a desired time span. The output side 9" of the gas piston thus applies the 
mechanical energy E.sub.m ' to the spring-loaded ratchet pawl 3 which, in 
turn, transfers this energy to the transport device 5 via the input 12 
thereof. The result is a marked simplification in the system, reduced wear 
and requiring fewer moving parts which require maintenance or repair. 
The markedly reduced number of moving parts required for the claimed system 
will be readily apparent from FIGS. 3-5 and the following description 
thereof. 
In FIG. 3 we have shown a portion of an automatic weapon in which only the 
parts essential to the invention have been illustrated in detail, the 
remaining portions being of the type generally described in said German 
patent and the literature cited therein including German Pat. No. 
1,126,282 and U.S. Pat. Nos. 2,501,143 and 2,815,699 to the extent that 
such elements are consistent with the structure described hereinafter. 
The weapon comprises the usual barrel 1' and a gun housing 1" aligned with 
the barrel 1'. The interior of the barrel and the chamber is represented 
by the reference numeral 1, previously indicated to identify the 
pressurizable space behind the projectile (see FIG. 2) with which a 
propellant-gas tap 6 in the form of a passage communicates. 
The passage 6, in turn, opens into an enlargement 7.0 of a gas passage in 
the housing. The gas passage 7 comprises a first branch 7.1 extending in 
the housing parallel to the axis A of the weapon and connected to a 
transverse branch 7.2 which is perpendicular to the axis A and opens into 
a gas reservoir or compartment 13 at the inlet 10'. 
The inlet 10' is surrounded by a centering body 17 forming a seating 
surface 18 for a tubular insert 14. The insert 14 is provided with an 
inlet region 14' with a circularly cylindrical recess 16 which 
communicates with an orifice 19' formed in an abutment shoulder 19 in the 
insert 14 which is perforated at 15 to communicate between the outer 
partition of the space 13 and the interior of this tubular insert. 
An end 14" of the insert 14 is press-fitted into a central recess 25 of a 
plug 24 threaded into the housing 1" of the weapon by a screw thread 26. 
The cylindrical recess 16 receives a valve body 20 which is shorter by the 
distance l than the distance between the surface 18 from the abutment 19. 
The valve body 20 is formed with a central bypass whose flow cross section 
is smaller than that of the orifice 19' and with at least one peripheral 
recess 22. In parallel with the gas reservoir 13 of the energy-storage 
unit 4', the cylinder/gas-piston arrangement 2 is provided with a 
cylindrical wall 29 forming a guide for the gas piston 9. 
The latter has a pressurizable side 9' and, at its opposite end, a guide 
portion 33 whose end face 9" engages the ratchet pawl 3. 
The guide cylinder 2' is closed at its end proximal to the ratchet pawl 3 
by a tubular threaded plug 30 whose screw thread 32 is connected with the 
housing 1" and whose interior forms a guide housing for the portion 33 of 
the piston 9. 
A passage 28 opens into the cylindrical wall 29 and connects the gas 
reservoir 13 outwardly of the insert 14 with the portion 8' of the 
cylinder at the gas-pressurizable side 9' of the piston. 
The latter is axially shiftable in a working stroke in the direction of the 
arrow H.1, the restoring stroke being represented by the opposite arrow 
H.2. 
The end face 9" is juxtaposed with a surface of the pawl 3 mentioned 
previously which is swingable as represented by the arrow W about an axis 
indicated at 34. 
The axis 34 is the axis of the stepping transport mechanism 5, e.g. its 
feed shaft, for the munitions belt of the weapon (see German Pat. No. 
1,292,455), the pawl 3 being urged in the clockwise sense by a restoring 
spring (not shown). The belt-advance mechanism is received in a housing 5' 
and is not further illustrated. 
The belt-feed system of the invention operates as follows: 
When a cartridge in the chamber of the weapon is fired, the propellant gas 
develops in a period of the order of milliseconds a considerable pressure 
behind the projectile which is driven from the barrel in the direction of 
the arrow S (FIG. 3). 
As soon as the projectile has passed the tap 6, for a brief period the 
propellant-gas pressure is applied through the passage 7 and a portion of 
the volume of this highly compressed propellant gas is led via the passage 
7 to the inlet region 10' of the energy-storage unit. The pressure 
upstream of the energy-storage unit, i.e. at the inlet 10', is represented 
by p.sub.v and over the aforementioned interval is significantly higher 
than the pressure p.sub.h downstream of the inlet 10'. 
The pressure gradient or differential is effective to drive the valve body 
20 practically instantaneously against the abutment shoulder 19 so that 
the propellant gas passes through the bypass 21 and the passage 23 defined 
by the recess 22 into the gas reservoir 13. A ratio a=p.sub.v /p.sub.h 
thus rapidly reahes the value of unity. 
As soon as the projectile has left the barrel, the pressure in space 1 
(hence the pressure p.sub.v ahead of the inlet region 10') drops rapidly 
to the atmospheric starting pressure. As a result of this reversal of the 
pressure gradient, the valve body 20 is displaced in the opposite 
direction of the distance l against its seat 18 so that only throttled 
flow of propellant gas through the bypass 21 is permitted. The reciprocal 
1/a reaches unity more slowly. 
The propellant gas which has been admitted to the reservoir 13 upon the 
development of the feed-pressure gradient favoring pressurization of the 
reservoir expands in the compartment 8' and shifts the gas piston 9 in the 
direction of its working stroke H.1. The end face 9" of the piston swings 
the ratchet pawl 3 along the arc W about its axis 34 to advance the 
cartridge-carrying belt in the usual manner. During the working stroke, a 
form-fitting connection is ensured between the pawl 3 and the input 
element 12 of the transport device 5 which can be the feed shaft mentioned 
previously. 
With each working stroke W of the ratchet pawl 3, the munitions belt is 
stepped through a full increment of its displacement to position the next 
cartridge at the chamber. The form-fitting connection between the pawl 3 
and the shaft is then interrupted and the pawl swings in the opposite 
sense (clockwise in FIG. 4) into its starting position, as shown, to shift 
the piston 9 in the direction of its return stroke H.2. 
The flow cross sections at 10' for pressurization and depressurization of 
the chamber 13 can be set optimally for the desired response rate of the 
munitions-belt feed. The timing is controlled by the conditions at the 
reservoir while the pneumatic energy is transformed simultaneously to 
mechanical energy at the mechanism 5, 12, 5'. The energy/time 
characteristic is selected in accordance with the firing characteristics 
of the weapon and thus as a function of the munitions used. However, the 
adjustment of the characteristic is relatively simple since the capacity 
of the energy-storage unit 4' can be advantageously modified in a simple 
manner. 
The capacity of the gas-storage volume, apart from that of the passage 7 
which can remain fixed, is controlled by the plug 27 which can be threaded 
into the plug 24 and which has been shown in dot-dash lines in FIG. 5. 
Naturally, other (measuring) means may be provided to indicate the 
effective volume of the compartment and to adjust it by effectively 
enlarging or decreasing the free space therein. The dimension l is 
adjusted by the plug 24.