IL33391A - Automatic or semi-automatic firearm - Google Patents

Description

OR Johnson Florida A automatlo or firearm having a different al recoil system in which an open b lt has designed mass and closing velocity to impact and drive a reoiprooating forwardly without rebound and remain looked to the barrel during the period when there is high iring pressure in the Since the bolt supports the cartridge during the time of high the cartridge is prevented from prematurely being extracted since recoil momentum is utilized in arresting and returning the stability of the firearm is invention relates to a more particularly to a firearm of the automatic or As is well recoil of any gun increases the or that part of it which is decreased weight or the of the ammunition that is ed is The reason is that a given cartridge will develop a oharacteristio amount of recoil given particular length of regardless of the type of the gun it fired the type This recoil momentum results in a kinetic energy of recoil or recoil energy proportionate to the square of the recoil momentum and varies inversely with the mass of the recoiling other doubling the recoil momentum by increasing the power of the cartridge will quadruple the recoil energy of the Reducing the mass on the other hand by fifty percent will double the recoil reducing the weight of a gun and creasing the power of the ammunitio substantially increases the recoil is a critical problem in stability of lightweight guns when firing powerful One system developed to this problem is called a differential recoil I one variation of this system the and breech are orced a recuperator spring before firing and held i this position b a or After the gun is loaded and the the and breech are then driven forwardly by the The recuperator spring is designed to impute to the masses of the barrel and breech a velocity that would be equal to that which would be tained in a conventionale other the spring would give the and breech a velocity to attain a forward momentum equal to of the normal recoi momentum the particular ammunition This forward momentum is attained s prior to the barrel and breeoh reaching their fully forward or battery At this the gun is Since moving masses at firing have a forward momentum approximately equal to of the recoil momentum which the cartridge is capable of of the produced by the cartridge is in arresting the forward motion of the breeoh and and the remaining half utilized throwing them rearwardly where they once again cought and held by the It important to note that at no time do the recoiling masses of the and breech contain more than the recoil momentum which would attained by a conventional gun of the same weight in its recoiling This important since the recoil energy is to the square of the momentum of the coiling in terms of recoil at no time does the barrel and breech oontain more than of the recoil energ of equivalent conventional In rather than impacting directly on the the recoil momentum is distributed during the movement of barrel and The stability of the gu is thereby greatly In automatic firearms this system has been generally alon two different basic In the first approach a conventional automatic weapon mechanism is in a weapon frame in a manner whioh the barrel a limited amount of motion alon the axis of the The weapon is fired from the open bolt and employs a conventional mechanically locked In suoh a which gas operated in usual an operating rod receives energy from a gas system subsequently and opens the bolt in customary weapon obtains the effect of differential recoil by permitting the barrel reciprocate within the frame without impact the the barrel being moved forwardly by the of operating rod and and then arrested and moved rearwardly by the mentum produoed by firing before an impaot with the frame can Weapons of this type are entirely conventional as to the method of looking and the method of obtaining energy for and differ from automatic weapons in having provisio for the breech medhanlsm and barrel to oscillate over a distance within frame of the weapon while This approach permits the weapon to attain the stability resulting from and does not special types of ammunitio ammunition but has the disadvantage of being necessarily complex The second approach which is frequently used of a kind in which the barrel is fixed to the weapon frame and does no participate in the A simple blowback type of bol is whioh is not meohanioall looked to the barrel at any weapon is fired from the open bolt and the cartridge is fired before reaohing fully forward position in the The motion of the case and the blowback bolt is then first arrested by the mentum caused by and then accelerated to the providing differ recoil in exactly the same manne previously except the bolt is the only reciprocating This type of weapon requires use of a speoial and a specially shaped cartridge oase permits the front portion of the bolt to ente the chamber with Since the cartridge base and bolt must be able to move within the ohamber during eriod when the propellent gas pressure is the cartridge oase must be heavily If this is not the forward portion of cartridge will to the wall of the ohamber because the oausih a separatio and consequently a may see from the foregoing that weapons which lize the differential reooil principle have either the disadvantage of being complex construction or the disadvantage of requiring the use of heavil lubricated diaadvantages have prevented the suooess of various attempts to apply the principle of reooil to automatic small arms of a type intended for individual although the advantages of diferential recoil in providing mildness of recoil effects and stability in fully automatic fire are highly desirable in this class of As is well the use of low powered ammunition in an automatic weapon the use of a blowbaok mechanism in which the bolt is the operating and in whio the bolt serves to look the action effectively through because of blowbaok it also serves as the operating energ In weapons employing such low powered the use of lubricated ammunition is not and the weapon accordingly ver simple and use of pressure of the type usually necessary or ri maohine guns and automatic prevents the use of the simple blowbaok system of and requires either the speoial and tion lubrication oommon to the system described or the of a mechanicall looked breech combined with a rate operating energy In the latter the weapon beoomes plex in design and and in less reliable than elementary blowbaok weapon which uses low powered Attempts have been made to produce a gun can fire high powered ammunition without the complicity of a meohanically looked breeoh but have been it is an object Of this invention to provide an automatic or firearm having an operating system whioh can safely an unlocked blowbaek Another object is to provide a stable automatio or another object is to provide an automatio or firearm having a system of operation in the bolt and barrel of the fi earm move together during a period of dangerous barrel to eliminate or greatly the of cartridge to tured by simultaneous adherence of the front portion of the oase to the wall of the chamber while the back portion is forced to the rear by further ob eot is to provide an automatio or firearm having system of operation in the bolt has a designed momentum to drive the barrel after the bolt oloaes against the such that of the firing reooil momentum is in arresting the forward motion of the bolt and lis in returning the bolt to its rearward A still further object is to provide an automatio or firearm having a system of operatio in which a barrel spring is to arrest the forward movement of the barrel and return it to its rearward Another is to provide an automatio or firearm having a system of operation whioh the barrel has a natural frequeno of vibration against barrel spring such that the barrel returned1 wardly simultaneously with the rearward stroke of the Another object is to provide an automatio or firearm having a system of operation in whioh propellent gas system arrests the forward movement of the barrel and returns it to its rearward Another object is to provide and automatio or firearm havin a system operation in which propeilant gases are trapped between the forward end of the frame to assist in arresting the ward movement of the barrel and then moving the barrel objeot s to provide an automatio or rearwardly with the holt during a period of high firing Another object is to provide an automatic or firearm having a system of in which the of the barrel is fluted to prevent the cartridge object to provide an automatic having system operation the bolt barrel a lo efficient of restitution or Another is to provide an automatic or firearm having of easy to field strip and Another lis to provide an automatic having operating system whioh not Another object is to provide firearm having a system of operation whioh Is unusuall simple but exceedingly Another object is to provide utomatic or firearm which is and economically feasible to Other object o the invention will in part be obvious and will i part appear In accordance these the invention comprises an automatic o In the firearm contains whioh houses a reoiprooally and both of along longitudinal In a oopked the boltis held to the rear of the frame the force of a driving spring by a the is to be the sear is triggered release At the bolt drives under the influence of the drive receives a and then inserts the cartridge into the When the bolt oloses against the barrel and cartridge is finall a firing pin protruding the face of the bolt fires the Simultaneously firing of the the mass and velocity is suoh that as it contacts pr impacts against the barrel it has a forward equal to mately firing recoil Upon impactin with the rearward The impaot of the bolt on the barrel to be of a type known as low doeffioient of restitution or In this type of the bolt and do not tend to after but rather in the bolt and barrel move immediately the ridge fired durin the dangerous period when there is high pressure in Since the bolt at this time efectively looked to the the bolt supports the rear of the oartridge is thereby prevented from stretched unacoeptabl or ruptured beoause the high After the bolt and have moved forwardly for a short distance the bolt begins to decelerate its forward movement due the gas pressure in the barrel acting on the bolt throug the rear of the cartridge The bolt is eventually stopped by the gas pressure and then rearwardly by this pressure and the bolt drive which had been over extended due to the forward momentum o Although the bolt moves rearwardly at this time barrel in its orward movement oausing the bolt and to apart in opposite at this the looking effeot botweon the bolt and barrel is at an This looking effeot designed suoh that the bolt and barrel remain together until the pressure the chamber sufficiently reduced to enable the oartridge to be extracted without being stretched or At the end of the looking the barrel continues its ward movement for distanoe until arrested b the barrel compression After the barrel lis thrust rearwardly b the barrel spring until to res in its initial rearward The bolt meanwhile continues to move rearwardly under the influence of the gas pressure and bolt drive As it moves it extracts and ejects the oartridge om the firearm in a oustomary If the firearm ia of the automatic variety the bolt may be held to the rea by the sear Upon reaching its full recoil in which the firearm is onoe again ready to be if the firearm is fully auto the bolt is simply permitted to retur and When the gun extremely of the coil momentum produced in firin the Oartridge is utilised in arresting the forward motion of the bolt and the other hal of the recoil is utilized in returning the to its initial since the forward movement of the barrel is cushioned the barrel neither the bolt the barrel have metal to with the fram and the frame therefore only subjected to spring Being subjected only to spring the frame and operator the firearm reoeive a low and relatively constant orce than successio of impacts as would be the without differential reooil Thus stability is a first modification of this the mass and barrel spring rate are adjusted so as to cause the barrel to have particular natural conjunction with barrel This frequenoy of vibration is designed that the time period correspondin to of a oomplete osolllation is approximately equal to the duration of the pressure period within the chamber of when the system is the spring exerts a foroe the barrel equal to but in an opposite direotion to the foroes tending to move the barrel When the moves rearwardly the spring also moves the barrel The result is that the limit of the lookin effec will be extended as the will not only travel forwardly with the bolt bt will also reverse and move with the bolt during rearward Since the bolt supports the oartridge oase over a longer period of time the tendency of the cartridge to stretch is even further In a muzzle in addition to the barrel spring of the primary embodiment are utilized to retard and the forward movement of the By so acting on the the muzzle gases effectively retard the separation of the bolt and barrel and prolon the looking effect of the bolt and Because of similar to the previous modification i which the barrel has a particular frequenoy of vibration the barrel the tendency of the cartridge oase to stretoh is substantiall In third a is utilized in place of a barrel When the cartridge propellent gases are passed into a compression between the barrel and the These acting similar to the barrel irst arrest the orward movement of the and drive the barrel to rearward In still another the system is arranged for olosed bolt In this the is initially in a forward position and moves rearwardly with the bolt when a cartridge The advantage of the differential recoil system is but sinoe the bolt supports the oartridge during the period of this system is beneficial when closed bolt firing is the may be fluted at the forward end so to permit gas on the outside of the oartridge case to counteract the gas pressure within the oartridge oase to still further eliminate any tendency of the oartridge to stretoh as the bolt and barrel begin to The invention accordingly comprises the features of bination of elements and arrangement of parts which will be exemplified in the oonstruotio hereinafter set and the soope of the invention will be indioated in the claims For a understanding of the nature and objects of the reference should be had to the followin detailed desorlptlon taken in nection with the accompanying drawings in whicht 1 is a elevation view of the firearm prising the 2 is a view of the firearm modified a Figures and 8 are views showing a sequential operation of the firearm of 9 shows a partial elevation view Of the firearm modified with a concentric 10 is a partial elevation of firearm modified with an gas 11 is a elevation view of the modified to enable the bolt to be fired from a olosed Figures 14 are views showing a sequential operation of the firearm of 15 is a elevation view of the firearm of 11 modified with an ffset gas 16 is partial elevation view of the modified with a fluted a end view the fluted ohamber taken along line of Similar reference oharaoters refer to similar parts throughout the several views of the Referring to drawings in particularly the is designated as 10 and a frame 12 housing a reoiprooall ted bolt and barrel Barrel 16 a barrel abutment IB slidably received within enlarged cylindrical ohamber 20 of frame A barrel spring 24 or barrel biasing means is disposed between abutment 18 and forward end wall of frame 12 to bias abutment 18 of barrel against an posterio wall 26 of c When abutment 18 against ohamber wall the barrel is rearward also hereafter sigaated as a first Δ conventional cartridge extractor 28 and firing pin 30 are contained o the forward end of bolt Disposed between the rear wall of the frame and the bolt is bolt drive spring 32 driyln the bolt forwardly against the This driving spring is designated to drive the b lt forwardl and cause the bolt to reaoh a velooity just before closing equal to proximatel that whioh would be normall reached if the fie where from a olosed That the holt is given a momentum equal of the firing reooil momentum of the oartridge being Between the bolt and the barrel is a conventional oartridge supply magazine 54 or other oartridge supply means for supplying cartridges to the bolt as it A customary sear sear spring and trigger 40 contain bolt cooked position in a manner is obvious and When bolt 14 ie bolt drive spring a compressed The operation of the firearm will be described following the tional sequenoe of 3 through The firearm is prepared be fired by cocking bolt 14 and holding the bolt the of driving spring 32 by sear The gun fired by releasing sear trigger Onoe the sear is bolt moves forwardly pickin up a ridge 41 from supply magazine and inserts oartridge into the When the oartridge is finally seated and the bolt opntaots or impacts against the as shown in firing pin fires the It should be noted that alternativel the bolt designed impaot on the oartridge and through the partridge the Impaot of the bolt on the barrel drives the barrel The bolt and barrel are designed so that this is that is the bolt barrel do not rebound after This design necessary to maintai the bolt and barrel in a looked position from the moment of firing until the firing pressure developed by the propellent gas is Some of the factors are considered in this design are the dampening effect of the cartridge entering the chamber and in forcin the projectile into initial engagement the the mephanioal effert pf forcin the extractor over the rim of the oartridge and the subsequent engagement of the extractor with the spring pr other dampening means may be between the bolt and barrel to further insure a The hae a velocity oh impact to give its mass a forward momentum equal to approximatel the reooil momentum of the particula patrtridge being The result that of the reooil from firing is utilized in arresting the forward movement and or the is utilized in returning it to its rearward The masses of bolt and barrel are also designed such that as the bolt impacts against the barrel and moves it forwardly against the barrel the barrel and bolt remain together during their forward movement the gas essure in chamber is sufficiently reduced to allow the oartrldge to be extracted without being ruptured or At shown in the forward motion has been arrested by the gas pressure which then reverses aocelerates the bolt barrel 16 oontihuss its forward movement for a short distance arrested by This position seen in hereafter re erred to as the forward or second as seen in barrel spring returns barrel to its rearward position and the oartrldge case is ejected a conventional manner as the bolt moves The bolt is held by the sear eaching the full recoil position if the firearm is to be of he in oase the firearm has returned to the position it in being If the is to be fully the bolt is simply permitted to return forwardly and repeat the With correot spring the spring energ capcity of bolt spring 32 and barrel spring 24 is sufficient to prevent either the bolt or barrel from having metal to metal impaot with frame while the cartridge is being since the reooil momentum acts only on the not on the the stability of the firearm is In the above as initial separation of the and barrel results as the continuing forward motion of the as to the of the if the forward motion of the barrel can be retarded and or possibly at the time the bolt gins its rearward separating from the the barrel would remain effectively looked to since the bolt remains with the barrel for a longer period o cartridge would be supported even durin the time when there is a low pressure in the barrel and any tendency of system to cartridge case would One method of extending the of the looking effect of barrel and bolt is by modifying the barrel In this the barrel mass and the spring rate are designed so as to cause the barrel to have a particular natural frequenoy pf vibration in conjunction with the barrel This fixed frequency of vibration is designed such that the time period corresponding to of the complete oscillation pf the barrel is approximately equal to the duration of the pressure period within the chamber of the when the firearm is the Spring will assist in retarding the forward motion of the barrel but will also reverse move the barrel rearwardly when the bolt moves the length during the bolt will be looked to the barrel substantia ally Sinoe the looking effect is the cartridge oase is supported by the bolt or a longer period of time until the pressure the ohamber further This causes the cartridge to be extracted after the pressure within the ohamber has subsided to a and the tendenc the cartridge oase to stretch is substantiall In second another method of prolonging the looking of the barrel and bolt is In this modification a muzzle system utilized seen i The firearm the same as the ment shown in with the that the frame 42 pf the firearm tends forwardly of the 44 and has frame end 46 threadably cured to its orward This end has a opening slightly larger than the projectile 49 to allow the to the opening without In as the projectile the pressure of the gas 47 expelled at the muzzle between the barrel and end plug 46 assists the barrel spring 24 to decelerate the forward motion of the ohamber is tapped the at a position as close as possible to the chamber to allo the gas pressure to aot the barrel as soon as possible after As the gas pressure pressure chamber it acts on barrel to first arrest or tard the for ard motion of the barrel then return the barrel to its rearward Forward barrel spring relatively is only utilized to ensure that the barrel is in its rearward first position at of the firing The advantage of utilising a gas system is that the gas pressure in the system force in proportion to the force bein applied to the bolt through the rear of the This enables the looking effect to be prolonged both the bolt and the rel are arrested in their forward movement simulatenously and then propelled rearwardly In lookin can be prolonged until the firing pressure subsides to a negligible The bolt after tion from the barrel continues to be propelled rearwardly by the gas the bolt spring exactly as previously It is essential that the be arranged to have a minimum initial volume when the is in its rearward position to insure the most rapid and matching of the In this modification the masses of the bolt and rel and the momentum imparted to the bolt are designed to insure tha momentum is utilized arresting the forwad movement of both the rel and bolt and in returning them to their initial As in the previous stability of the fi earm is improved since the coiling parts in the frame and metal to metal impact the frame is In of the gas as shown in instead of a concentric ported gas system of an or eccentric gas system is In this system the barrel supports on its lower face a cylindrical housing 63 open at one end and communicating at its closed end with the interior of the barrel through propellent gas port Slidably received within housing 63 lis a piston on an end In operation the components are in proper relationship for firing as shown in At this barrel spring biases barrel housing 74 against piston This is the forward or first position of the After bolt 88 is closed against the the not of the firearm triggered causing the firing pin to fire the dartridge in conventional When the cartridge is gas pressure ing into the compression chamber acts on the closed end of housing 74 ing the barrel to mote The gas system is designed to exert a force on the barrel to overcome various forces which tend to move the barrel orwardl such as the initial engraving of the ling the forwardly moving the projectile friotipn force and if a necked type oartridge the forwrd exerted the gas pressure on the shoulder of the The system is also designed to accelerate mass rearwardl at a rate equal to the acceleration of the whioh is rearwardly by propellent gas pressure acting on the rea of the Since the gas pressure does force the barrel baok at a rate to the rearward acceleration the the barrel and bolt are effectively together during their rearward This looking effect is designed to continue until the pressure within the chamber of the barrel subsides sufficiently to allow the oartridge to be At this the barrel stops when arrested by barrel spring whioh is the rearward or second The bolt however continues to be prop to the seen in until the gas pressure The oartridge is ejected from the weapon a conventional manner on the rearwrd After the gas pressure subsides barrel spring 86 returns the barrel to its ward position and boit drive spring 90 returns the bolt against barrel The bolt receives and inserts a cartridge into the chamber of the barrel on its forward stroke whereupon the firearm is again ready to be Obviously the advanatages of the diferential reooil system as mentione the preferred embodiment and modifications thereof is this closed bol gas is of value to prevent the cartridges from being overly stretched when closed bolt firing is Instead of an compression the bolt gas system may be provided with chamber shown in system similar to the structure shown in the barrel is formed annular barrel shoulde rides i a cylindrical chamber formed by the barrel in with an lar rearward wall 9 and a annular forward end wall of f me The forward portion of the chamber between shoulder and forward 98 herea referred to as an expansible ohamber Immediatel shoulder or gas ports 104 arranged around the oiroumferenoe high pressure gas from the interior of the barrel to pressure chambe Ports 104 lie immediately forward of the chamber to insure that propellent gas pressure be received in pressure chamber as soon the oartridge is As an additional means to that a oartridge case is hot stretched beyond an acceptable a fluted barrel ohamber ma be employed with an of above embodiments or modifications As seen in Figures 16 ohamber 106 of the barrel 108 is with shallow longitudinal flutes 110 disposed along forward portion of the The drawin for exaggerates the depth and Width of the flutes Being that the chamber is propellent gas pressures both on interior and exterior of the forward position of the oartridge case Where the flutes are This substantially the area over which the internal firing ipressure to force the cartridge against the chamber The adherence of the oartridge oase to the wall durin high firing pressure is accordingly Although the firing means fo the above embodiments and modifications thereof consisted of a conventional firing pin oh the end of the it should be understood that other conventionale means of firing oartridge may be employed suoh as eleotrlo primed a ated It should be evident from the above description that a novel firearm has been developed whioh has a number of distinct dvantages he prio The utilises a operating whioh provides for effective lookin and operating energy supply without the use of a ventional looking system and energ supply That is the barrel and bolt are in mechanically free This accomplished by designing a blowback bolt with a particular mass and closing velocity and a cating barrel with a particular These components are designed that impaots against the barrel without rebound and drives it forwardly while remaining in close contact with the barrel until high firing pressure within the chamber substantially Since the bolt supports the rear of the cartridge oase during the period of high firing the oartrldge does not stretch or fracture and tions of that type are The momentum at impact with the barrel is approximately of the firing recoil of the ridge being of the recoil movement is utilized to arrest the forward movement of the bolt and the remaining half to drive the bolt back to is rearward A barrel spring first arrests the forward movement of the barrel and then returns the barrel to its initial This enables the gun extremely stable even when firing high powered ammunition since there Is no metal to metal with the Several modifications of the invention are One of these modifications uniquely a barrel and barrel spring combination which is designed to cause the barrel to have a natural frequenoy of vibration against the barrel spring suoh that the barrel spring will move the barrel rearwardly simultaneously with the bolt to extend the time during whioh the barrel and bolt are effectively looked Since the time is cartridge is finally in another a similar result may he utilized with a muzzle booster in which gases are trapped between barrel and frame to retard the forward movement of the barrel and move it earwardly with the The firearm ma also easily be adapted gas system in of the barrel spring1 to retain the same Further if it to use the firearm with a olosed bol firing firearm may be modified with a gas system which causes the barrel to move rearwardly with the bolt until firing pressure in the chamber has sufficiently subsided to extract the cartridge without Undue The firearm is extremely utilizing a of ting Because of its the firearm is eas to field strip and repair as as being ver practioal and eoonomioall feasible to For simplicity and ease of understanding the Inventive racteristics of the the firearm and its various modifications have been illustrated the drawings with only the essential operating parts exaot nature of the assembl of other than that d to the in 1 it should be obvious that a provision must be made i frame 12 to remove or insert barrel One such obvious provision would be to thread the end In suoh obvious although it should be understood that the firearm is designed to enable its various parts to be assembled and It will thus be seen that object set forth among those made apparent from the preceding are eficiently attained since certain may be made in the above construction departing from scope it is intended that all matter contained the above description or shown in the drawing shall be as illustrative and not in a limiting It is to be understood that the following claims are intended to cover all of the and tures of the Invention herein and all statements of the scope of the invention as a matter of might be said to fall insufficientOCRQuality

Claims (9)

1. 33391/2 Claims A firearm comprising: A frame, a bolt reciprocally mounted along the longitudinal axis of said frame, a barrel reciprocally mounted along the longitudinal axis of said frame between a first and second position, said bolt having a cartridge receiving means for receiving and inserting a cartridge in the chamber of said barrel and a cartridge extracting means for extracting said cartridge after being fired, firing means for firing said cartridge, a bolt drive spring disposed to drive said bolt forwardly, barrel biasing means to bias said barrel toward said first position, cartridge supply means for supplying a cartridge to said bolt, said bolt arranged to receive the cartridge on its forward stroke and afterwards insert the cartridge into the chamber of said barrel, said cartridge fired when in said chamber by said firing means, said bolt being biased into operative engagement with said barrel when said cartridge is fired, said bolt and said barrel in mechanically free engagement relative to each other, a gas system means for controlling the movement of said barrel relative to said frame and returning said barrel to said first position, said gas system means including at least one propellant gas port in said barrel adjacent the forward end of the chamber of said barrel, said gas system means further including an expansible compression chamber, said expansible compression chamber disposed between a portion of said barrel and a portion of said frame, said compression chamber in communication with said propellant gas port whereby when said cartridge is fired, propellant gas enters said compression chamber and acts on said barrel portion to arrest the movement of the barrel relative to said frame and simultaneously moves said barrel 33391/2 rearwardly with said bolt said bolt moving rearwardly undjer the rearward force of said cartridge such that the relative motion between said bolt and said barrel is zero whereby ^ said bolt and said barrel remain in mechanically-free contact during at least a portion of their rearward movement*

2. The firearm of Claim 1 wherein longitudinal flutes are disposed on said chamber to substantially balance the firing pressure on both sides of the cartridge.

3. The firearm of Claim 1 wherein said barrel portion comprises a concentric barrel shoulder integral with said barrel, said shoulder reciprocally riding in a cylindrical opening between said barrel and forward and rearward annular walls of said frame, said expansible compression chamber formed between said shoulder and the forward annular wall of said frame.

4. The firearm of Claim 1 wherein said barrel portion comprises : a cylindrical barrel housing carried by said barrel, said housing parallel to tjie longitudinal axis of said barrel, said housing closed at its rearward end, a piston riding in said housing, one end of said piston contacting said frame, and said expansible compression chamber formed between said closed end of said housing and said piston.

5. The firearm of Claim 1 wherein said frame extends forwardly to said barrel, said frame having a forward end wall adjacent the forward end of said barrel, said end wall having an opening to pass a projectile from said barrel, firing gases from firing said projectile acting on the end of said barrel to assist in arresting the forward movement of the barrel and moving tfee barrel rearwardly with the bolt to enable said bolt and barrel to continuously remain in mechanically-free contact during, their 33391/2 (

6. The firearm of Claim 5 wherein longitudinal flutes are disposed in said chamber to substantially balance the firing pressure on both sides of the cartridge.

7. · The firearm of Claim 1, said firearm being fired from a closed bolt position, said barrel bein forward when in said first position, an opening in said barrel adjacent the forward end of the chamber of the barrel for passing propellant gases, said opening in communication with an expansible pressure chamber, said chamber including a portion of said barrel whereby when a cartridge is fired propellant gas pressure acts on said barrel portion and simultaneously acts on said bolt through the rear of the cartridge to simultaneously move said bolt and barrel rearwardly while in said mechanically-free contact until the high firing pressure within the chamber of the barrel substantially subsides.

8. The firearm of Claim 7 wherein longitudinal flutes are disposed in said chamber to substantially balance the firing pressure on both sides of the cartridge.,;

9. A firearm, substantially as hereinbefore described with reference to the accompanying drawings. For the Applicant Dr. Yitzhak Hess.