US3219022A

US3219022A - Pneumatic gun for surgical use

Info

Publication number: US3219022A
Application number: US234915A
Authority: US
Inventors: Harrison P Hagemeyer
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-10-31
Filing date: 1962-10-31
Publication date: 1965-11-23
Anticipated expiration: 1982-11-23

Description

Nov. 30, 1965 H. P. HAGEMEYER PNEUMATIC GUN FOR SURGICAL USE Filed Oct. 31, 1962 INVENTOR. HARRISON P- HAGEMEYER Mam ATTORNEYS Y B w m n N Ea: mo: Enid/l1! hh fiwlf h mwvkikm w m N. 2 9 3 m l g m t m 7/ T M v w W m v United States Patent 3,219,022 PNEUMATIC GUN FOR SURGICAL USE Harrison P. Hagemeyer, 6601 Brendon Lane, Silver Hill, Md. Filed Oct. 31, 1962, Ser. No. 234,915 6 Claims. (Cl. 124-11) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to pneumatic guns for projecting of light weight fine diameter missiles, more particularly shafts of animal hair into aneurysms of the brain.

Aneurysms of the brain are bubble-like deformities which appear in the walls of arteries at weakened points. The repetitive pounding of blood in the artery thins out the wall of th aneurysm. In time, the dome of the sac begins to leak. The patients life is in a precarious position during this period, because the flow of blood from the dome of the aneurysm is restrained by only a tiny clot in the opening. Any acut rise in arterial blood pressure or any direct mechanical stress of the weakened sac is fraught with disaster. If the aneurysm should rupture, the intercranial cavity becomes flooded with arterial blood; with fatal result.

In the past, aneurysms of the brain have been treated by the application of a tiny V-shaped silver clip around the neck of the sac. The clip is so placed that the main stream of the artery on which the aneurysm is situated is not interrupted. This method of handling an aneurysm has been frequently successful. However, in a significant number of cases, closure of the clip around the pulsating neck of the aneurysm causes the artery wall to break at that point. When this happens, the surgeon has no choice but to arrest the hemorrhag by occluding the parent vessel on either side of the aneurysm. In some cases, this has led to fatal swelling of th brain, and in others, to paralysis of the extremities on one half of the body. Still another problem arises when treatment with clips is attempted: manipulation of this treacherous lesion, in order to find its neck, can easily dislodge the tiny clot plugging the opening of the dome.

It is for the above reasons that such techniques as lowering the patients temperature to critical levels (hypothermia), dropping the blood pressure to critical levels (hypotension) and shutting oif the circulation to the brain for short periods (extra corporeal pump) have been devised in recent years. These radical measures tend to make the treatment of intercranial aneurysm a little safer, but some of them require rather formidable and expensive equipment.

The ideal surgical objective is to destroy the aneurysm without manipulating it. The generation of a clot inside th aneurysm by the insertion of a foreign body, such as a hair, has seemed to be a positive answer to the problem.

Mammalian hair, including human hair, has a rough, horny exterior, resembling the scales of a fish. The scales, or projections from the hair surface, are pointed up toward the tip of the hair. Neurosurgeon John P. Gallagher postulated that the introduction of a hair into an artery or vein would cause the blood around the hair to clot immediately. After several days, scar tissue was expected to invade the clot and anchor it in place permanently. He proposed to introduce hair into aneurysms of the brain to induce clotting of the blood for obliteration of the aneurysm. However, manual introduction of such foreign body into an aneurysm might move it and cause rupture. Consideration was given, therefore, to the possibility of delivering the hair into the aneurysm 3,219,022 Patented Nov. 23, 1965 under high velocity by means of a gun, the muzzle of the gun to be held against the aneurysm when fired. A spring actuated gun was found rough in its action and to involve too much manipulation of the mechanism and too much weight to be a safe instrument for the purpose. Its use would be fraught with danger to the patient. The use of a direct air jet (blow gun) for driving the hair into an aneurysm of the brain was found to rupture the aneurysm and damage the brain.

The present invention has as an object the provision of a pneumatic gun by which a light weight fine diameter material, such as an animal hair, can be smoothly pro jected under high velocity.

It i also an object to provide a pneumatic gun of this kind which is almost totally without recoil and can be employed for delivering a shaft of animal hair into a brain aneurysm without fatal disturbance of the aneurysm. It is also an object to provide a novel missile barrel assembly for a pneumatic gun of the kind aforesaid.

The above and other objects will be more fully understood by reference to the following detailed description taken in conjunction with the accompanying drawing in which is shown by way of illustration, a preferred form of construction of the pneumatic gun in accordance with my invention.

In the drawing in which like numerals indicate like parts:

FIGURE 1 is a view in section of the pneumatic gun in accordance with a preferred embodiment thereof,

FIGURE 2 is a view in section of the pneumatic gun showing the relative position of certain parts after the gun has been fired. gun has been fired,

FIGURE 3 is a detail view of a part for the pneumatic gun, and

FIGURE 4 is a detail view in section of the construction of the part as shown in FIGURE 3.

The pneumatic gun as shown in the drawing consists, generally speaking, of two detachably connected sections, the one a pneumatic propulsion unit and the other a missile projector unit. The propulsion unit is arranged in communication with the missile projection unit so as to cause a fine lightweight missile such as a stout animal hair to be pushed at high velocity from the bore of the projection unit to enter and lodge in an aneurysm of the brain.

Referring to FIGURE 1 and the pneumatic propulsion section of the gun, the tube 1 has an elongated tubular pneumatic propulsion or firing chamber 25 in which is contained a primary plunger 2 adapted for pneumatic propulsion therein by application thereto of air or other suitable gas under high pressure. The plunger 2 has an integrally attached, forwardly extending finger 3 in axial alignment therewith, the function of which will be hereinafter described.

In the missile projection section of the pneumatic gun, the detachable barrel 4 has a cylindrical recess 5 and a fine diameter missile bore 8 in communication with the recess 5 and axially aligned therewith. A secondary or follower plunger 6 is contained in the cylindrical recess 5 for lengthwise movement therein. The length of the plunger 6 is such as to provide suflicient bearing surface of the plunger on the wall of the cylindrical recess 5 as to hold the finger 7 in true alignment with the missile bore 8 for passage therein. For this purpose the ratio of the length to diameter of the plunger 6 may be from about 1V22 /3:1 and preferably is 2%:1. Attached to the plunger 6 and in axial alignment therewith, is a forwardly extending finger 7 adapted to slide in the missile bore 8 on forward movement of the plunger 6 in the cylindrical recess 5. The length of the finger 7 is greater than the full travel distance for the plunger 6 in the cylindrical recess 5 and not greater than the length of the missile bore 8. Thus, th combined length of the plunger 6 and finger 7 is greater than the length of the cylindrical recess 5 whereby the finger 7 extends into the bore in the assembled, firing condition of the gun to provide for front loading of the missile barrel and contact of the lightweight fine diameter missile with the finger 7 when the gun is fired.

Suitable means for detachably connecting the missile barrel 4 to the firing chamber 25 is provided in the form of a head type bushing 9 inset and brazed in the end of the tube 1. The bushing and missile barrel are appropriately threaded for detachably securing the missile barrel to the tube. The arrangement of the bushing in the tube is such as to provide axial alignment of the cylindrical recess 5 with the firing chamber 25 in the assembled condition of the missile barrel 4 and tube 1. To the end of insuring this axial alignment, the inside face of the base of the bushing 9 is machined to present a fiat shoulder 10 to the squared end of the missile barrel 4 in assembly of the parts. The base of the bushing defines the forward wall of the firing chamber 25, which chamber is made of sufiicient length that the primary plunger 2 may have sufficient travel distance therein to attain to a high enough speed on firing that the finger on the follower plunger 6 can push the hair or other lightweight fine diameter missile from the bore 8 at high velocity.

A passageway 11 is provided in the base of the bushing 9 which is in axial alignment and communication with the firing chamber 25 and cylindrical recess 5 in the assembled arrangement of the tube 1 and missile barrel 4. The passageway 11 is defined by a sleeve liner 12 fitted into an aperture of appropriate diameter. The finger 3 of the a,

primary plunger 2 moves through the passageway 11 in the course of the operation of the gun. The diameter of the passageway is larger than the diameter of the finger 3 for a function which will appear hereinafter.

In the assembled condition of the pneumatic gun, the L primary plunger 2 is held in the cocked position in the firing chamber 25 by a suitable releasable holding means which, as shown, is a conventional spring-loaded balldetent mechanism. The ball-detent 15 rests in a circumferential shallow groove 1.4 in the plunger 2 and is held in the groove by the pressure of the spring 16. The load on the spring 16 may be varied by rotation of the cap 17.

The plunger 2 is released and propelled by application thereto of air at a pressure sufficient to override the spring load on the ball detent. Air is prevented from passing forward of the plunger 2 by means of the O-ring 18 of silicone rubber which is inset in the circumference of the plunge. The inner wall of the tube 1 is lapped to provide a true surface in the firing chamber 25 for the O-ring. Air

under pressure for driving the plunger 2 may be supplied to the tube 1 in any known or conventional way. As shown, air under pressure is delivered to the firing chamber behind the primary plunger 2 through the pipe 19 which is attached to the tube 1 by the flanged coupling 20; a flexible hose, e.g., Tigon tubing (not shown) capable of withstanding the pressure of the air being connected to the pipe 19 from a source of compressed air (not shown).

The pneumatic gun is set up for operation by assembling the follower plunger 6 in the cylindrical recess 5 of the missile barrel 4 such that the plunger extends out of the recess 5 for a short distance. The projector unit so assembled is then inserted in the bushing 9 in the forward end of the tube 1, the threading engaged, and the missile barrel turned into the secured position with the end of the missile barrel abutting flush with the flat shoulder 10 in the bushing 9. In the course of setting the missile barrel into position in the bushing 9, the plunger 6 will be pushed back and positioned in the rearward section of the cylindrical recess 5 and the forward end of the attached finger 7 will extend into the missile bore 8 to provide a front loading missile barrel into which the fine missile, a stiff animal hair, is loaded by inserting it, tip first, into the bore until contact has been made with the forward end of the finger 7. The pneumatic propulsion section of the gun has in the meantime been prepared for firing by connecting the tube 19 to a suitable source of compressed air and setting the plunger 2 in the cocked position in the firing chamber under the predetermined holding load imposed by the spring loaded ball detent mechanism.

FIGURE 2 shows the position of the moving parts of the pneumatic gun after it has been fired and the fine missile, hog hair 24, projected from the bore 8 at high velocity. The primary plunger 2 has been impelled in the firing chamber 25 to the extremity of travel therein and the attached finger 3 has advanced through the passageway 11 to contact the follower plunger 6 and push it through the full travel distance therefor in the cylindrical recess 5. The finger 7, being attached to the plunger 6, is pushed through the full travel distance therefor in the bore 8 to push the hair 24 from the bore at high velocity.

The pneumatic gun is made almost totally without recoil in operation by venting from the gun air which is compressed in the firing chamber 25 ahead of the moving primary plunger 2 and in the cylindrical recess 5 ahead of the moving follower plunger 6. A suitable means for accomplishing this involves the use of vent holes in the wall of the tube 1 near the forward end of the firing chamber 25 which are in air flow communication with means on the surface of the follower plunger 6 for back fiow of air from ahead of this plunger in the cylindrical recess 5. A series of holes 13 in the wall of the tube 1 allow venting of air from the firing chamber 25 as it is compressed ahead of the propelled primary plunger 2. These vent holes 13 communicate through the passageway 11 for flow of air thereto from means on the follower plunger 6 for release of compressed air from ahead of this plunger in the cylindrical recess 5. The passageway 11, as described above, has a diameter larger than the diameter of the finger 3 whereby when the finger is in the passageway in operation of the gun, an air channel exists through the passageway for flow of compressed air from the cylindrical recess 5 to the vent holes 13.

Means on the follower plunger 6 for venting of air compressed in the cylindrical recess 5 ahead of the moving plunger 6 is shown in detail in FIGURE 3. As there shown, a series of shallow grooves 21, which may be of any suitable cross-sectional geometry, are provided in the surface of the plunger, from end to end, whereby the air compressed in the recess 5 can flow back through these grooves to and through the channel in the passageway 11 fol]; venting from the gun through the holes 13 in the tu e 1.

FIGURE 4 is a detail view of the construction involved in securing the fine diameter finger 7 to the plunger 6. The finger '7 which may be of piano wire .008 inch diameter, is secured in the plunger 6 by inserting one end of the wire through an axially aligned hole, .010 inch diameter, in the plunger and shaping this end against the forward and upper sides of the cylindrical recess 22. The wire is secured in the recess 22 by means of the plug 23, which may be of brass or other suitable material, which is driven into the recess behind the wire as shown. In a particular embodiment of the pneumatic gun as described above, the tube 1 is of steel, 7 inches in length, has an outside diameter of inch and an inside diameter of 3 inch. Including the head of the bushing 9, the total overall length of the tube is 7% inches. The bushing 9 is a head type steel bushing, 4 inch in length and Z4 inch in internal diameter. The passageway 11 in the base of the bushing is X inch in diameter and the copper sleeve liner 12 has an outside diameter of {lag inch. The holes 13 (four in number) are of ovoidal shape measuring 3 inch across in the lengthwise direction of the tube and inch across in the transverse direction of the tube. These holes are located in an area of the wall of the tube which is directly back of the interior end of the bushing 9. The primary plunger 2 of steel has a length of inch and a diameter of inch. The integral steel finger 3 has a length of inch and a diameter of 55, inch. The O-ring 18 is suitably made of silicone rubber and is x inch. In the missile projecting section of the gun, the barrel 4 or brass is inch long and has inch outside diameter for /2 inch of its length from which point it tapers to a blunt point of inch width. The cylindrical recess 5 has a diameter of inch and a length of /2 inch. The missile bore 8 is /5 inch in length and of capillary diameter, which to accommodate an animal hair such as horse hair or hog hair is .007 to .010 inch. The follower plunger 6 of steel is inch long and inch in diameter. The end to end grooves on the surface of the plunger 6 are 1 inch V-shaped grooves. The finger 7 of piano wire is .008 inch in diameter and inch long which allows the finger to extend into the missile bore, of inch, for front loading of the missile barrel with a shaft of hair which can be A inch in length.

The pneumatic gun of the invention in the particular embodiment described above has been used successfully in delivering shafts of hog and horse hair into aneurysms of the brain which have resulted in obliteration of the aneurysm and full recovery of patients who have been declared to have a nonoperable condition. In all cases, the gun was held against the aneurysm, when fired. The hair is propelled tail first into the aneurysm with the scales lying grainwise or fiat against the body of the hair as it enters the wall of the aneurysm. This procedure avoids tearing of the wall of the aneurysm by scales which would stand out from the body of the hair if the hair were to be propelled tip first into the aneurysm. By using a finger on the follower plunger in the missile barrel which is slightly shorter than the length of the missile bore, the hair can be propelled into the aneurysm and yet leave a short end section outside of the aneurysm as a tell-tale to indicate the presence of the hair in the aneurysm.

While the pneumatic gun has been described for use in surgery where it has proven highly successful, it may be used for non-surgical purposes where it is desired to propel fine diameter lightweight missiles, e.g., shafts of gold, silver, sttel, etc., into bodies susceptible of receiving them.

Since various changes and modifications may be made in the invention without departing from the spirit or scope thereof, it is intended that the preferred embodiment appearing in the above description shall be taken by way of illustration rather than in limitation except as may be required by the appended claims.

What is claimed is:

1. A pneumatic gun capable of projecting lightweight fine diameter missiles at high velocity which comprises in combination:

a detachable missile barrel having a cylindrical recess and a missile bore of fine diameter extending from and communicating with said cylindrical recess and in axial alignment therewith,

said cylindrical recess being of greater length and diameter than said missile bore,

a follower plunger slidably fitting in said cylindrical recess for lengthwise movement therein,

said follower plunger having a forwardly extending finger of a length greater than the full length of travel of said follower plunger in said cylindrical recess but not greater than the length of said missile bore and slidably fitting in said missile bore,

said follower plunger having a ratio of length to diameter of from about 1 /2 to 2%:1 to provide sufficient bearing surface on the Wall of said cylindrical recess to hold the finger on said follower plunger in true alignment with said missile bore,

said follower plunger and finger having a combined length greater than said cylindrical recess for extending said finger part way into said missile bore to form a front loading missile barrel when said follower plunger and finger are assembled in said cylindrical recess in the firing condition of the gun,

said follower plunger being adapted on forward movement through the full travel distance therefor in said cylindrical recess to push said finger through the full travel distance therefor in said missile bore,

pneumatic means including a tube having an elongated tubular pneumatic propulsion chamber and a primary plunger slidably fitting in said chamber for pneumatic propulsion therein detachably connected to said missile barrel and in operative communication with said cylindrical recess for rapidly pushing said follower plunger through the full travel distance therefor in said cylindrical recess,

said pneumatic means further including means for sealing the portion of said pneumatic propulsion chamher which is forward of said primary plunger against flow of propulsion gas thereinto in operation of the and means for venting from the gun at the forward end of said pneumatic propulsion chamber during operation of the gun the air which is compressed ahead of said plungers in operation of the gun.

2. A pneumatic gun as defined in claim 1,

having a cylindrical passageway between said pneumatic propulsion chamber and said cylindrical recess and in axial alignment therewith,

and a forwardly extending finger on said primary plunger in axial alignment with said passageway and constituting means to pass through said passageway to push said follower plunger through the full travel distance therefor in said cylindrical recess.

3. A pneumatic gun as defined in claim 2,

wherein the means for venting from the gun air which is compressed ahead of said primary plunger and said follower plunger in operation of the gun includes openings in the wall of said tube at the forward end of said pneumatic propulsion chamber,

end to end grooves in the surface of said follower plunger in said cylindrical recess,

and means forming an air flow channel in communication with said tube wall openings and said end to end grooves in the surface of said follower plunger.

4. A pneumatic gun as defined in claim 3,

wherein the means for forming said air flow channel in communication with the tube Wall openings and the end to end grooves in the follower plunger includes the forwardly extending finger on said primary plunger and said cylindrical passageway of a diameter larger than that of said finger on said primary plunger.

5. A pneumatic gun capable of projecting lightweight fine diameter missiles at high velocity which comprises in combination,

a tube having an elongated tubular pneumatic propulsion chamber,

means in said tube for inset detachable connection of a missile barrel to the forward end of said tube,

said means in said tube for inset detachable connection having a wall transverse of said tube which defines the forward wall of said pneumatic propulsion chamber,

a missile barrel having a cylindrical recess and a missile bore of fine diameter extending from and communieating with said cylindrical recess and in axial alignment therewith,

said missile barrel having means for being inset and detachably connected to the forward end of said tube with said cylindical recess adjacent to and in axial alignment with said pneumatic propulsion chamber,

said follower plunger having a ratio of length to diameter of about 2%:1,

said follower plunger having a forwardly extending finger of a length greater than the full length of travel of the follower plunger in said cylindrical recess but not greater than the length of said missile bore and slidably fitting in said missile bore,

said follower plunger being adapted on forward movement through the full travel distance therefor in said cylindrical recess to push said finger the full travel distance therefor in said missile bore,

a cylindrical pasageway through said tranverse wall communicating with said pneumatic propulsion chamber and said cylindrical recess and in axial alignment therewith,

a primary plunger slidably fitting in said pneumatic propulsion chamber for pneumatic propulsion therein,

means for sealing the portion of said pneumatic propulsion chamber which is forward of said primary plunger against flow of propulsion gas thereinto in operation of the gun,

said primary plunger having a forwardly extending finger in axial alignment therewith,

said primary plunger finger being of a smaller diameter than said passageway and constituting means to pass through said passageway to push said follower plunger through the full travel distance therefor in said cylindrical recess, and

means for venting from the gun during operation of the gun the air which is compressed ahead of said plungers in operation of the gun,

said venting means including openings in the wall of said tube at the forward end of said pneumatic propulsion chamber in air flow communication through said passageway with end to end grooves in the surface of said follower plunger.

6. A pneumatic gun for projecting lightweight fine diameter missiles at high velocity which comprises in combination:

5 said follower plunger having a ratio of length to diameter of from about 1 to 2%,;21 to provide sufi lcient bearing surface on the wall of said cylindrical recess to hold the finger on said follower plunger in true alignment with said missile bore,

said follower plunger and finger having a combined length greater than the length of said cylindrical recess for extending said finger part way into said missile bore to form a front loading missile barrel when said follower plunger is assembled in said cylindrical recess in the firing condition of the gun,

said follower plunger being adapted on forward movement through the fulll travel distance therefor in said cylindrical recess to push said finger the full travel distance therefor in said missile bore,

pneumatic means detachably connected to said missile barrel and in operative communication with said cylindrical recess for rapidly pushing said follower plunger through the full travel distance therefor in said cylindrical recess,

said pneumatic means including a tube having an elongated tubular pneumatic propulsion chamber,

a primary plunger slidably fitting in said chamber for pneumatic propulsion therein,

a cylindrical passageway between said pneumatic propulsion chamber and said cylindrical recess and in axial alignment therewith,

said primary plunger having a forwardly extending finger in axial alignment therewith and constituting means to pass through said passageway to push said follower plunger the full travel distance therefor in said cylindrical recess,

means including openings in the Wall of said tube at forward end of said pneumatic propulsion chamber for venting from the gun at the forward end of said pneumatic propulsion chamber during operation of the gun the air which is compressed ahead of said plungers in operation of the gun, and

said sealing means including an elastic ring located on and attached to said primary plunger.

References Cited by the Examiner UNITED STATES PATENTS 1,591,756 7/1926 Guidote l24l1 2,554,116 5/1951 Monner 124--l1 55 RICHARD (J. PINKHAM, Primary Examiner.

Claims

1. A PNEUMATIC GUN CAPABLE OF PROJECTING LIGHTWEIGHT FINE DIAMETER MISSILES AT HIGH VOLOCITY WHICH COMPRISES IN COMBINATION: A DETACHABLE MISSILE BARREL HAVING A CYLINDRICAL RECESS AND A MISSILE BORE OF FINE DIAMETER EXTENDING FROM AND COMMUNCIATING WITH SAID CYLINDRICAL RECESS AND IN AXIAL ALIGNMENT THEREWITH, SAID CYLINDRICAL RECESS BEING OF GRATER LENGTH AND DIAMETER THAN SAID MISSILE BORE, A FOLLOWER PLUNGER SLIDABLY FITTING IN SAID CYLINDRICAL RECESS FOR LENGTHWISE MOVEMENT THEREIN, SAID FOLLOWER PLUNGER HAVING A FORWARDLY EXTENDING FINGER OF A LENGTH GREATER THAN THE FULL LENGTH OF TRAVEL OF SAID FOLLOWER PLUNGER IN SAID CYLINDRICAL RECESS BUT NOT GREATER THAN THE LENGTH OF SAID MISSILE BORE AND SLIDABLY FITTING IN SAID MISSILE BORE, SAID FOLLOWER PLUNGER HAVING A RATIO OF LENGTH TO DIAMETER OF FROM ABOUT 1 1/2 TO 2 2/3: 1 TO PROVIDE SUFFICIENT BEARING SURFACE ON THE WALL OF SAID CYLINDRICAL RECESS TO HOLD THE FINGER ON SAID FOLLOWER PLUNGER IN TRUE ALIGNMENT WITH SAID MISSILE BORE, SAID FOLLOWER PLUNGER AND FINGER HAVING A COMBINED LENGTH GREATER THAN SAID CYLINDRICAL RECESS FOR EXTENDING SAID FINGER PART WAY INTO SAID MISSILE BORE TO FORM A FRONT LOADING MISSILE BARREL WHEN SAID FOLLOWER PLUNGER AND FINGER ARE ASSEMBLED IN SAID CYLINDRICAL RECESS IN THE FIRING CONDITION OF THE GUN, SAID FOLLOWER PLUNGER BEING ADAPTED ON FORWARD MOVEMENT THROUGH THE FULL TRAVEL DISTANCE THEREFOR IN SAID CYLINDRICAL RECESS TO PUSH SAID FINGER THROUGH THE FULL TRAVEL DISTANCE THEREFOR IN SAID MISSILE BORE, PNEUMATIC MEANS INCLUDING A TUBE HAVING AN ELONGATED TUBULAR PNEUMATIC PROPULSION CHAMBER AND A PRIMARY PLUNGER SLIDABLY FITTING IN SAID CHAMBER FOR PNEUMATIC PROPULSION THEREIN DETACHABLY CONNECTED TO SAID MISSILE BARREL AND IN OPERATIVE COMMUNICATION WITH SAID CYLINDRICAL RECESS FOR RAPIDLY PUSHING SAID FOLLOWER PLUNGER THROUGH THE FULL TRAVEL DISTANCE THEREFOR IN SAID CYLINDRICAL RECESS, SAID PNEUMATIC MEANS FURTHER INCLUDING MEANS FOR SEALING THE PORTION OF SAID PNEUMATIC PROPULSION CHAMBER WHICH IS FORWARD OF SAID PRIMARY PLUNGER AGAINST FLOW OF PROPULSION GAS THEREINTO IN OPERATION OF THE GUN, AND MEANS FOR VENTING FROM THE GUN AT THE FORWARD END OF SAID PNEUMATIC PROPULSION CHAMBER DURING OPERATION OF THE GUN THE AIR WHICH IS COMPRESSED AHEAD OF SAID PLUNGERS IN OPERATION OF THE GUN.