Gas-operated device for activating the reloading mechanism of a gas-operated automatic rifle

A gas-operated device for activating the reloading mechanism of an automatic rifle comprising a cylinder housing and a movable piston, both mounted coaxially upon a cartridge store, the whole assembly being affixed below the rifle barrel. Gases from a cartridge exploded in the rifle breech are bled from the barrel through a duct into an annular chamber between the piston and a closed end of the cylinder to drive the piston and activate the reloading mechanism. Immediately prior to this bleeding, gases are bled through an additional duct into an interstice between the piston and the cylinder to act as a `gaseous diaphragm` preventing leakage of the driving gases from the annular chamber, except when the pressure of these driving gases is excessively high.

BACKGROUND OF THE INVENTION 
The present invention relates to a gas operated device for activating the 
reloading mechanism of an automatic rifle. More particularly, to such a 
device comprising a cylinder fixed to the rifle barrel and having a closed 
end and an open end, a piston slidable in the cylinder, and a chamber 
formed within the cylinder between the piston and the closed end, the 
chamber communicating with the interior of the rifle barrel through a gas 
duct. 
In known gas-operated devices of the above type, firing gases generated by 
the explosion of a cartridge in the rifle breech are bled off from the 
rifle barrel, through the gas duct, into the chamber between the piston 
and the closed end of the cylinder. The pressure of these gases operates 
the piston which in turn activates the reloading mechanism. The pressure 
of the gases which operate the piston depends on the explosive power of 
the cartridge, since the cartridges available commercially for use in 
sporting rifles vary widely in their quantity of power, the pressures on 
the piston also vary widely. Therefore, in order for such gas-operated 
devices to operate under the varying conditions, and particularly with low 
pressures of the order of 90-100 atmosphere, the reloading mechanism is 
usually especially designed to operate at such low pressures and maximum 
use is made of the energy of the gases by providing precision-made 
mechanical seals between the cylinder and piston. 
This method of achieving a seal between the cylinder and piston has a 
number of disadvantages. Firstly, the making and assembly of such 
mechanical seals having the required degree of precision is extremely 
difficult and laborious. Secondly, due to the precision and tightness of 
the seal, when a cartridge giving high pressure firing gases (180 - 200 
atmospheres) is used, the mechanical stresses exerted on the reloading 
mechanism of the rifle are so high that they can result in breakage, 
deformation or jamming of the mechanism. If the mechanism is not broken, 
the high pressure firing gases would at least reduce the working life of 
the mechanism considerably. 
In order to overcome the above disadvantages, compensating and/or 
regulating devices, which absorb the excess kinetic energy of the piston, 
or selectively operable mechanical compensators which compensate for the 
different thrusts upon the piston, or pressure relief valves which 
discharge the excess pressure of the diverted gases, may be incorporated 
in such gas-operated rifles. The use of any of these compensating and/or 
regulating devices, complicates the functioning of the rifle and may make 
the mechanism even more prone to jamming, however, these devices do not 
ensure the desired safe functioning of the rifle however accurate the 
assembly and adjustment of the devices. 
Therefore, an object of the present invention is to provide a gas-operated 
device for activating the reloading mechanism of an automatic rifle which 
may be used with a wide range of commercially available cartridges but 
which does not incorporate mechanical seals in the cylinder-piston 
coupling, nor involve the use of mechanical compensating or regulating 
devices. 
According to the present invention there is provided a gas-operated device 
for activating the reloading mechanism of an automatic rifle, comprising a 
cylinder fixed to the rifle barrel, and having an open end and a closed 
end, a piston slidable in the cylinder, and a chamber formed within the 
cylinder between the piston and the closed end, the chamber communicating 
with the interior of the rifle barrel through a first gas duct, 
characterised in that there is provided an interstice coaxial with and 
between the piston and the cylinder, the interstice communicating with the 
said chamber and opening through at least one second gas duct into the 
interior of the rifle barrel at a position closer to the breech end of the 
barrel than the opening of the first gas duct into the rifle barrel. 
Preferably, the piston has an annular groove in its surface such that in 
the fully inserted position of the piston in the cylinder, the or vents 
vent of the second gas duct into the interstice is opposite the groove. 
When a cartridge is fired from a rifle equipped with a device according to 
the present invention portions of the firing gas are bled successively 
into the interstice between the cylinder and the piston and into the 
chamber between the piston and the closed end of the cylinder. Within the 
interstice and the chamber the gases expand, thereby lowering the 
pressure, to values dependent upon the respective volumes of the 
interstice and the chamber. The gases beld into the chamber attempt to 
escape through the interstice, but escape is prevented by the 
counterpressure of the gases bled previously into the interstice. Thus a 
`gaseous diaphragm` is created in the interstice which acts as a seal 
against the release of the gases from the chamber and results in almost 
total exploitation of the energy of these gases for moving the piston and 
operating the reloading mechanism of the rifle. 
The position of the gaseous diaphragm in the interstice varies according to 
the value of the firing-gas pressure at the openings to the gas ducts in 
the rifle barrel, the relative dimensions of the gas ducts, the volume of 
the interstice between piston and cylinder, the volume of the chamber 
formed between the piston and the closed end of the said cylinder, and 
according to the ratio of these volumes. In practice, the dimensions of 
the ducts, interstice and chamber being predetermined, therefore, the 
position of the `gaseous diaphragm` in the interstice depends exclusively 
upon the pressure of the firing gases. When this pressure is low (90-100 
atmospheres), the `gaseous diaphragm` is formed very close to the chamber 
but as the pressure of the firing gases increase the position of the said 
diaphragm moves towards the open end of the cylinder. When the pressure of 
the firing gases is very high (180-200 atmospheres) the counterpressure of 
the gases diverted directly into the interstice, while still impeding the 
escape of the gases diverted into the chamber, is no longer able to act as 
a gaseous sealing diaphragm. The gases can therefore escape, to a limited 
degree, through the interstice, so that the pressure on the piston is 
reduced, with consequent reduction of the force exerted by the piston on 
the reloading mechanism of the rifle. 
Other objects and further scope of applicability of the present invention 
will become apparent from the detailed description given hereinafter; it 
should be understood, however, that the detailed description and specific 
examples, while indicating preferred embodiments of the invention, are 
given by way of illustration only, since various changes and modifications 
within the spirit and scope of the invention will become apparent to those 
skilled in the art from this detailed description.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings, a barrel of a gas-operated automatic rifle is 
shown at 1 and a cartridge store which extends parallel to and below the 
barrel 1, in normal use of the rifle, is shown at 2. 
A cylinder 4, affixed to the barrel 1 by known means (not shown), is 
assembled coaxially upon the store 2. The cylinder 4 is open at one end 7 
towards the rifle breech (not shown), but the clearance between the 
cylinder 4 and the cartridge store 2 at the opposite end of the cylinder 
4, nearer the muzzle of the rifle, is sealed by a sealing ring 5, 
effectively closing this end of the cylinder 4. 
Also assembled coaxially upon the store 2 and within the cylinder 4 is a 
piston 8, one end of which extends through the open end 7 of the cylinder 
4 and is provided with a flange 9. Between the opposite end of the piston 
8 and an internal shoulder 4a of the cylinder 4 is an annular chamber 10 
which communicates with the interior of the barrel 1 through a gas duct 11 
in a common wall of the barrel 1 and the cylinder 4. 
Extending from the annular chamber 10, between the opposing cylindrical 
walls of the piston 8 and the cylinder 4, is an interstice 12 which 
communicates with the interior of the barrel 1 through a further gas duct 
13 in the common wall of the barrel 1 and the cylinder 4. The gas duct 13 
opens into the interstice 12 through a vent 13a and opens into the barrel 
1 at a position closer to the rifle breech than the duct 11. An annular, 
rectangular-section groove 14 is provided in the external surface of the 
piston 8 immediately opposite the vent 13a of the duct 13, in the fully 
inserted position of the piston 8 in the cylinder 4, shown in FIG. 1. The 
piston 8 is further provided with a number of radial through-holes 17 
through which the clearance space between the piston 8 and the cartridge 
store 2 communicates with the interstice 12. 
A movable sleeve 15 having an annular head 16 which cooperates with the 
flange 9 of the piston 8 is also assembled coaxially upon the store 2. The 
sleeve 16 is connected by known means (not shown) to the reloading 
mechanism (not shown) of the rifle and is urged towards the cylinder and 
piston assembly by resilient means (not shown). 
When a cartridge is exploded in the rifle breech, the cartridge (not shown) 
is thrust along the barrel 1 by the firing gases and first clears the 
entrance to the duct 13, allowing a portion of the firing gases to escape 
through the duct 13 into the interstice 12 and the annular groove 14. 
Immediately thereafter the cartridge clears the entrance to the duct 11, 
and a further portion of the firing gases escapes into the chamber 10. The 
expansion of the gases in the chamber 10 forces the piston 8 towards the 
breech, the piston 8 encountering and pushing the sleeve 15 which operates 
the reloading mechanism of the rifle. 
As the portion of the gases bled into the chamber 10 expand the gases 
attempt to escape through the interstice 12 and are prevented by the 
counterpressure in the interstice 12 due to the gases previously bled from 
the barrel 1 through the duct 13. This cunterpressure effectively creates 
a `gaseous diaphragm` which constitutes a seal between the opposing 
surfaces of the piston 8 and cylinder 4. 
The value of the counter-pressure and hence the position of the said 
gaseous diaphragm in the interstice 12, depends on numerous factors, among 
which are the pressure of the firing gases at the openings to the ducts 11 
and 13 in the barrel 1, the dimensions of the ducts 11 and 13, the volume 
of the space formed by the interstice 12 and the annular groove 14 and the 
volume of the chamber 10. Since, in the device according to the invention, 
these dimensions and volumes are predetermined, the value of the 
counter-pressure and hence the position of the gaseous diaphragm in the 
interstice 12 depends on the pressure of the firing gases at the openings 
to the ducts 11 and 13 in the barrel 1. When this pressure is low (90-100 
atm.), the pressure of the gas diverted into the chamber 10 and the 
counter-pressure of the gas in the interstice 12, will be such that the 
said gaseous diaphragm will be positioned in the interstice 12 close to 
the chamber 10. When the pressure of the firing gases at the openings to 
the ducts 11 and 13 in the barrel 1 is increased, the difference between 
the pressures of the gases diverted into the chamber 10 and those diverted 
into the interstice 12 and the annular groove 14 is also increased, so 
that the position of the `gaseous diaphragm` is moved towards the open end 
7 of the cylinder 4. When the pressure of the firing gases at the openings 
to the ducts 11 and 13 in the barrel 1 is very high (180-200 atm.), the 
difference between the said pressures of the diverted gases is so 
negligible that no further `gaseous diaphragm` is formed in the interstice 
12, thus a portion of the gases diverted into the chamber 10 through the 
duct 11 can overcome the counter-pressure in the interstice 12, and can 
escape through the open end 7 of the cylinder 4. This escape of gas 
reduces the thrust of the gases in the chamber 10 on the piston 8, and 
hence reduces the mechanical stresses which result from the total 
exploitation of the energy of these gases as they are exerted on the 
reloading mechanism of the rifle. Thus a gas-tight seal is achieved in the 
cylinder-piston connection without the aid of washers or like mechanical 
seals. Also a certain degree of automatic adjustment of the stresses 
exerted upon the reloading mechanisms is achieved. 
In addition, a similar gas-tight seal is achieved in the clearance between 
the piston 8 and the cartridge store 2 by the presence in this clearance 
of a pressure generated by the gases diverted through the radial holes 17. 
The construction dimensions of a typical embodiment of a device according 
to the present invention are given below. 
A cartridge of restricted power, but generating a pressure of the firing 
gases at the openings to the ducts 11 and 13 of not less than 90 
atmospheres, was used in a 12 caliber gas-operated automatic sporting 
rifle including two gas ducts 11 located at a distance of 250 mm from the 
breech of the rifle. It was found that the gas-operated device according 
to the invention functioned as described above with the following 
dimensions: 
ducts 11 -- diameter 2.5 mm 
duct 13 -- diameter 2.5 mm and positioned at a distance of about 15 mm from 
the ducts 11; 
interstice 12 -- formed by a clearance of 0.15 mm between the piston 8 and 
the cylinder 4; 
chamber 10 -- volume of 2000 mm.sup.3 ; 
annular groove 14 -- volume of 200 mm.sup.3. 
Such variations are not to be regarded as a departure from the spirit and 
scope of the invention, and all such modifications as would be obvious to 
one skilled in the art are intended to be included within the scope of the 
following claims.