Automatic air rifle

Abstract

A receiver of an automatic air rifle includes a front sliding sleeve including upper and lower recesses; a main biasing member secured to the front sliding sleeve and the charging handle respectively; a roller; an L-shaped rod; a rear diversion channel through the front sliding sleeve; a rear sliding sleeve including pivotal upper and lower hooks; a main tube through the rear sliding sleeve and including a rear inlet and an annular flange proximate the rear inlet; a gas piston disposed forwardly of the main tube; an inlet member at a rear end of the gas piston; and an auxiliary biasing member put on the main tube and biased between the front sliding sleeve and the rear sliding sleeve. The air rifle is capable of firing in semi-automatic or fully automatic position.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to air rifles and more particularly to a feeding mechanism of an automatic air rifle having improved characteristics.

2. Description of Related Art

A conventional automatic firearm capable of automatic or semiautomatic fire is comprised of a receiver having a moveable hammer located therein; a selector rotatably mounted in the receiver, a first sear rotatably mounted in the receiver to engage the hammer, the first sear contacting a first camming surface of the selector; a second sear rotatably mounted in the receiver to engage the hammer, the second sear contacting a second camming surface of the selector; and a disconnect rotatably mounted in the receiver, the disconnect contacting a third camming surface of the selector. The selector has a number of selectable positions so that rotation of the selector between a first position and a last position of the selectable positions is less than 180 degrees.

While the device enjoys its success in the market, continuing improvements in the exploitation of feeding mechanism of an air gun of rifle type are constantly sought.

SUMMARY OF THE INVENTION

It is therefore one object of the invention to provide an automatic air rifle capable of automatic and semiautomatic fire comprising a receiver; a hollow limit member secured to a rear portion of the receiver; a spring-actuated cup member disposed in the limit member; an elongated cavity disposed in the receiver; a receptacle disposed at a front end of the cavity; an air chamber disposed at a rear end of the cavity; a fire control selector rotatably mounted on the receiver, the fire control selector being configured to rotate to point to a safe position, a semi-automatic position, or a fully automatic position; a cam member disposed in the receiver and co-rotated with the fire control selector; a first spring-biased member disposed to the left of the cam member; a second spring-biased member disposed to the right of the cam member; a spring-biased trigger pivotably secured to the receiver; a spring-biased pivotal member partially disposed in the trigger; a charging handle retractably disposed in the receiver; a front sliding sleeve disposed in a forward portion of the cavity and including an upper recess at a rear end and a lower recess under the upper recess; a main biasing member spaced from the front sliding sleeve, the main biasing member secured to the receiver and the charging handle respectively; a roller rotatably disposed in the cavity; an L-shaped rod disposed in the cavity; a rear stop member disposed at an end of a short part of the L-shaped rod and between the cam member and the second spring-biased member; a front stop member disposed at an end of a long part of the L-shaped rod; a rear diversion channel formed through the front sliding sleeve; a rear sliding sleeve disposed rearward of the front sliding sleeve and including a spring-biased, pivotal upper hook and a spring-biased, pivotal lower hook; a main tube disposed through the rear sliding sleeve and having a rear end slidably disposed in the cup member, and a front end fastened in the front sliding sleeve, the main tube including a rear inlet and an annular flange disposed forwardly of the rear inlet; a gas piston disposed forwardly of the main tube and forwardly of the front sliding sleeve, the gas piston having a front end disposed in the receptacle; a magazine releasably secured to the receiver and including a column for storing at least one pellet wherein one of the at least one pellet is pushed to contact an outer surface of the front end of the gas piston; a barrel having a rear end communicating with the front end of the gas piston; an inlet member formed at a rear end of the gas piston; and an auxiliary biasing member put on the main tube and biased between the front sliding sleeve and the rear sliding sleeve; wherein in response to rotating the fire control selector to the semi-automatic position, the cam member is disposed perpendicular to both the first and second spring-biased members, the rear stop member is not urged by the cam member, a pulling of the charging handle pulls the front sliding sleeve to be proximate the main tube, the gas piston moves rearward to allow one of the at least one pellet to enter the receptacle, the main biasing member expands, the upper hook lockingly engages the upper recess, the lower hook lockingly engages the lower recess, the auxiliary biasing member compresses, a releasing of the charging handle compresses the main biasing member to push both the front and rear sliding sleeves forward, the gas piston moves forward to push one of the at least one pellet into a rear end of the barrel, the upper hook is pressed by the roller in the forward movement of the rear sliding sleeve to disengage from the upper recess, a pulling of the trigger counterclockwise rotates both the pivotal member and the lower hook to unlock the front sliding sleeve, the auxiliary biasing member expands to push the rear sliding sleeve rearward, the main tube moves rearward to compress the cup member until the flange contacts the limit member and the rear inlet communicates with the air chamber, pressurized gas flows through the barrel via the air chamber, the rear inlet, the main tube, and the gas piston to discharge one of the at least one pellet out of the barrel, a portion of the pressurized gas flows into the diversion channel to push the front sliding sleeve rearward by compressing the auxiliary biasing member and expanding the main biasing member, the gas piston moves rearward to allow a next one of the at least one pellet to enter the receptacle, a stop of flowing the pressurized gas pushes the cup member forward to disengage the rear inlet from the air chamber, the upper hook lockingly engages the upper recess, the lower hook lockingly engages the lower recess, a pulling of the trigger counterclockwise rotates the pivotal member and moves the pivotal member along an outer surface of the lower hook without counterclockwise rotating the lower hook, the main biasing member compresses to push the rear sliding sleeve forward and compress the auxiliary biasing member, the upper hook is pressed by the roller in the forward movement of the rear sliding sleeve to disengage from the upper recess, and a release of the trigger clockwise rotates the pivotal member to disengage from the lower hook to dispose the trigger in a ready position; and wherein in response to rotating the fire control selector to the fully automatic position, the cam member is disposed perpendicular to both the first and second spring-biased members, the rear stop member is not urged by the cam member, a pulling of the charging handle pulls the front sliding sleeve to be proximate the main tube, the gas piston moves rearward to allow one of the at least one pellet to enter the receptacle, the main biasing member expands, the upper hook lockingly engages the upper recess, the lower hook lockingly engages the lower recess, the auxiliary biasing member compresses, a releasing of the charging handle compresses the main biasing member to push both the front and rear sliding sleeves forward, the gas piston moves forward to push one of the at least one pellet into a rear end of the barrel, the upper hook is pressed by the roller in the forward movement of the rear sliding sleeve to disengage from the upper recess, a pulling of the trigger counterclockwise rotates both the pivotal member and the lower hook to unlock the front sliding sleeve, the auxiliary biasing member expands to push the rear sliding sleeve rearward, the main tube moves rearward to compress the cup member until the flange contacts the limit member and the rear inlet communicates with the air chamber, first pressurized gas flows through the barrel via the air chamber, the rear inlet, the main tube, and the gas piston to discharge one of the at least one pellet out of the barrel, a portion of the first pressurized gas flows into the diversion channel to push the front sliding sleeve rearward by compressing the auxiliary biasing member and expanding the main biasing member, the gas piston moves rearward to allow a next one of the at least one pellet to enter the receptacle, a stop of flowing the first pressurized gas pushes the cup member forward to disengage the rear inlet from the air chamber, the upper hook lockingly engages the upper recess, the lower hook lockingly engages the lower recess, the main biasing member compresses, the auxiliary biasing member compresses to push the rear sliding sleeve forward, the upper hook is pressed by the roller in the forward movement of the rear sliding sleeve to disengage from the upper recess, a pulling of the trigger counterclockwise rotates both the pivotal member and the lower hook to unlock the front sliding sleeve, the auxiliary biasing member expands to push the rear sliding sleeve forward, the upper hook is pressed by the roller in the forward movement of the rear sliding sleeve to disengage from the upper recess, the pivotal member pivotably pushes the lower hook to disengage from the lower recess, the auxiliary biasing member expands to push the rear sliding sleeve rearward, the main tube moves rearward to compress the cup member until the flange contacts the limit member and the rear inlet communicates with the air chamber, second pressurized gas flows through the barrel via the air chamber, the rear inlet, the main tube, and the gas piston to discharge one of the at least one pellet out of the barrel, a portion of the second pressurized gas flows into the diversion channel to push the front sliding sleeve rearward by compressing the auxiliary biasing member and expanding the main biasing member, the gas piston moves rearward to allow a next one of the at least one pellet to enter the receptacle, a stop of flowing the second pressurized gas pushes the cup member forward to disengage the rear inlet from the air chamber, the upper hook lockingly engages the upper recess, the lower hook lockingly engages the lower recess, the main biasing member, the main biasing member expands, the auxiliary biasing member compresses, and both the front and rear sliding sleeves move forward to dispose the trigger in a ready position.

The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of an automatic air rifle according to the invention;

FIG. 1A is a detailed view of the area in a rectangle of FIG. 1;

FIG. 2 is a longitudinal sectional view of the bolt carrier in the receiver but shown in an acute angle;

FIG. 3 is a longitudinal sectional view of the bolt carrier in the receiver showing the fire control selector rotated to the semi-automatic position in a first firing mode;

FIG. 4 is a view similar to FIG. 3 showing the gas piston pushed backward, the main spring expanded, and a round pushed upward to a ready position by pulling the charging handle rearward;

FIG. 5 is a view similar to FIG. 4 showing the gas piston pushed forward, the main spring compressed, and the round pushed forward a small distance by releasing the charging handle;

FIG. 6 is a view similar to FIG. 5 showing the trigger being pulled to start a firing process;

FIG. 7 is a view similar to FIG. 6 showing the round being fired at the end of pulling the trigger;

FIG. 8 is a view similar to FIG. 7 showing a portion of the gasses being diverted to push the front sliding sleeve rearward, and a new round being pushed upward after firing the round;

FIG. 9 is a view similar to FIG. 8 showing the gas piston being pushed backward and the new round pushed to a ready to fire position;

FIG. 10 is a view similar to FIG. 9 showing the trigger being pulled and actions of other associated components;

FIG. 11 is a view similar to FIG. 10 showing the trigger being released and actions of other associated components;

FIG. 12 is a view similar to FIG. 11 showing the trigger and other associated components in a ready to fire position;

FIG. 13 is a view similar to FIG. 1A showing the fire control selector rotated to the automatic position in a second firing mode;

FIG. 14 is a longitudinal sectional view of the bolt carrier in the receiver showing the fire control selector in the automatic position;

FIG. 15 is a view similar to FIG. 14 showing the gas piston pushed backward, the main spring expanded, and a round pushed upward to a ready position by pulling the charging handle rearward;

FIG. 16 is a view similar to FIG. 15 showing the charging handle being released and the front sliding sleeve being moved forward, and the round being ready;

FIG. 17 is a view similar to FIG. 16 showing the gas piston pushed forward, the main spring compressed, and the round pushed forward a small distance after releasing the charging handle;

FIG. 18 is a view similar to FIG. 17 showing the trigger being pulled to start a firing process;

FIG. 19 is a view similar to FIG. 18 showing the round being fired at the end of pulling the trigger;

FIG. 20 is a view similar to FIG. 19 showing a portion of the gasses being diverted to push the front sliding sleeve rearward, and a new round being pushed upward after firing the round;

FIG. 21 is a view similar to FIG. 20 showing the gas piston being pushed backward, and the new round pushed to a ready to fire position;

FIG. 22 is a view similar to FIG. 21 showing the trigger and actions of other associated components;

FIG. 23 is a view similar to FIG. 22 showing a portion of the gasses being about to divert to the push the front sliding sleeve rearward and actions of other associated components after firing;

FIG. 24 is a view similar to FIG. 23 showing the portion of the gasses being diverted to the push the front sliding sleeve rearward and actions of other associated components after firing;

FIG. 25 is a view similar to FIG. 24 showing the front sliding sleeve being locked by the rear sliding sleeve due to the diversion of the gasses;

FIG. 26 is a view similar to FIG. 25 showing the trigger being returned to its inoperative position; and

FIG. 27 is a view similar to FIG. 26 showing the front sliding sleeve and the rear sliding sleeve being unlocked after the trigger returning to its inoperative position.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 to 27, an automatic air rifle in accordance with the invention comprises the following components as discussed in detail below in which a first firing mode of the air rifle is discussed in FIGS. 1 to 12.

A receiver 1 is provided. An elongated internal cavity 11 is provided in the receiver 1. A receptacle 12 is provided at a front end of the cavity 11. An air chamber 13 is provided at a rear end of the cavity 11. A fire control selector 14 is rotatably mounted on the receiver 1. The fire control selector 14 can be rotated to point to a “SAFE” (i.e., at which the air rifle cannot be fired) mode, a “SEMI” (i.e., semi-automatic) mode, or an “AUTO” (i.e., fully automatic) mode. A cam member 15 is provided in the receiver 1 and co-rotated with the fire control selector 14. A first spring-biased member 151 is provided to the left of the cam member 15 and a second spring-biased member 152 is provided to the right of the cam member 15 respectively (see FIG. 2). An exposed trigger 16 is pivotably secured to the receiver 1. The trigger 16 is pivotal because, at least, a forward spring 17 is provided in a front portion and a rear spring 19 is provided in a rear portion. The rear spring 19 is biased between the trigger 16 and a pivotal member 18 which is rearward of the rear spring 19. A charging handle 10 is provided in the receiver 1 and exposed so that a user may pull or push the charging handle 10. A front sliding sleeve 2 is provided in a forward portion of an intermediate portion of the cavity 11. A main spring 20 is provided above the front sliding sleeve 2. The main spring 20 has one end fastened in the receiver 1 and the other end secured to the charging handle 10 which in turn is secured to the front sliding sleeve 2. Thus, the charging handle 10 is made a spring-actuated member and the front sliding sleeve 2 is configured to move in response to compression or expansion of the front sliding sleeve 2.

A roller 21 is provided on an upper portion of the cavity 11. An L-shaped rod 3 is provided on a lower portion of the cavity 11. A rear stop member 31 s provided at an end of the short part of the L-shaped rod 3. The rear stop member 31 is disposed between the cam member 15 and the second spring-biased member 152 and contacts the same respectively. A front stop member 32 is provided at an end of the long part of the L-shaped rod 3. The front sliding sleeve 2 has a forward part and a rear part having a diameter less than that of the forward art. A diversion channel 22 is formed through an intermediate portion of the front sliding sleeve 2 joining the forward part and the rear part of the front sliding sleeve 2. A rear sliding sleeve 4 is provided rearward of the front sliding sleeve 2 and includes a spring-biased, pivotal upper hook 41 configured to lockingly engage an upper recess 23 at a rear end of the front sliding sleeve 2, and a spring-biased, pivotal lower hook 42 configured to lockingly engage a lower recess 24 at the rear end of the front sliding sleeve 2. A main tube 5 is provided through the rear sliding sleeve 4 and has a rear end fastened in a spring-actuated cup member 71 at a rear portion of the receiver 1. The cup member 71 is fastened in a hollow limit member 7 which is secured to the rear portion of the receiver 1. A front end of the main tube 5 is fastened in the front sliding sleeve 2. An inlet 51 is provided proximate the rear end of the main tube 5. An annular flange 52 is provided adjacent to the rear end. The flange 52 is between a rear end of the upper hook 41 and a rear end of the lower hook 42. A gas piston 54 is provided forwardly of the main tube 5. The gas piston 54 has a front end in the receptacle 12 and a substantial portion disposed in the front sliding sleeve 2. A pellet 53 stored in a column 61 of a magazine 6 is pushed to contact an outer surface of the front end of the gas piston 54. A barrel 50 has a rear end in communication with the front end of the gas piston 54. An inlet 55 is provided at a rear end of the gas piston 54. An auxiliary spring 40 is put on the main tube 5 and biased between the front sliding sleeve 2 and the rear sliding sleeve 4. Thus, the front sliding sleeve 2 is made into a spring-actuated member.

The first firing mode is discussed be low. In response to rotating the fire control selector 14 to the “SEMI” position (see FIG. 1A), the cam member 15 is disposed upright as shown in FIG. 3. The rear stop member 31 is not urged by the cam member 15. Next, a user may pull the charging handle 10 to pull the front sliding sleeve 2 (i.e., moving rearward) to a position proximate the front end of the main tube 5 (see FIG. 4). The gas piston 54 moves rearward a short distance to allow the pellet 53 to enter the receptacle 12. And in turn, the main spring 20 expands. Also, the upper hook 41 lockingly engages the upper recess 23 and the lower hook 42 lockingly engages the lower recess 24. Also, the auxiliary spring 40 is compressed. This is a ready to fire position. After releasing the charging handle 10, the main spring 20 compresses to push both the front sliding sleeve 2 and the rear sliding sleeve 4 forward. And in turn, the gas piston 54 moves forward to push the pellet 53 into a rear end of the barrel 50 to be ready to fire. The upper hook 41 is pressed by the roller 21 in the forward movement of the rear sliding sleeve 4. Thus, the front end of the upper hook 41 clears the upper recess 23 (see FIG. 5). The user may pull the trigger 16 to counterclockwise rotate the pivotal member 18. The counterclockwise rotation of the pivotal member 18 counterclockwise rotates the lower hook 42, thereby unlocking the front sliding sleeve 2 (see FIG. 6). The auxiliary spring 40 then expands to push the rear sliding sleeve 4 rearward (see FIG. 7). The main tube 5 moves rearward to compress the cup member 71 until the flange 52 contacts the limit member 71, and the inlet 51 communicates with the air chamber 13. Pressurized gas from an air canister (not shown) flows to the air chamber 13 and in turn flows through the main tube 5 via the inlet 51. And in turn, the gas flows through the gas piston 54 to discharge the pellet 53 out of the barrel 50 to fire. At the same time, a portion of the gas flows into the diversion channel 22 to push the front sliding sleeve 2 rearward by compressing the auxiliary spring 40 and expanding the main spring 20 (see FIGS. 7, 8 and 9). And in turn, the gas piston 54 moves rearward to unblock the top opening of the column 61, resulting in a new pellet 53 being pushed upward into the receptacle 12 to be ready for a next firing. Gas is stopped from supplying to the air chamber 13. The cup member 71 is pushed forward due to the expansion of the elastic component thereof. The flow path from the air chamber 13 to main tube 5 via the inlet 51 is blocked due to the disengagement the inlet 51 from the air chamber 13. Further, the upper hook 41 lockingly engages the upper recess 23 and the lower hook 42 lockingly engages the lower recess 24. This loading of pellet is automatic. Next, as shown in FIGS. 10 and 11, the user may pull the trigger 16 to cause the pivotal member 18 to counterclockwise rotate. The counterclockwise rotation of the pivotal member 18 compresses the rear spring 19 so that the pivotal member 18 may moves along the outer surface of a lower portion of the lower hook 42 without counterclockwise rotating the lower hook 42. The main spring 20 then compresses to push the rear sliding sleeve 4 forward, thereby compressing the auxiliary spring 40. The upper hook 41 is pressed by the roller 21 in the forward movement of the rear sliding sleeve 4. Thus, the front end of the upper hook 41 clears the upper recess 23. The user may release the trigger 16 to expand the rear spring 19, thereby clockwise rotating the pivotal member 18 to disengage from the lower hook 42 to return to the ready position (see FIG. 12).

As shown in FIGS. 13 to 27, a second firing mode of the air rifle is discussed below. In response to rotating the fire control selector 14 to the “AUTO” position (see FIG. 13), the cam member 15 is disposed horizontal as shown in FIG. 14. The rear stop member 31 moves rearward to be clamped by and between the cam member 15 and the second spring-biased member 152. The lower hook 42 is not supported by the pivotal member 18. Next, a user may pull the charging handle 10 to pull the front sliding sleeve 2 (i.e., moving rearward) to a position proximate the front end of the main tube 5 (see FIG. 15). The gas piston 54 moves rearward a short distance to allow the pellet 53 to enter the receptacle 12. And in turn, the main spring 20 expands. Also, the upper hook 41 lockingly engages the upper recess 23 and the lower hook 42 lockingly engages the lower recess 24. Also, the auxiliary spring 40 is compressed. This is a ready to fire position. After releasing the charging handle 10, the main spring 20 compresses to push both the front sliding sleeve 2 and the rear sliding sleeve 4 forward. And in turn, the gas piston 54 moves forward to push the pellet 53 into a rear end of the barrel 50 to be ready to fire (FIG. 17). The upper hook 41 is pressed by the roller 21 in the forward movement of the rear sliding sleeve 4. Thus, the front end of the upper hook 41 clears the upper recess 23. The user may pull the trigger 16 to counterclockwise rotate the pivotal member 18 (see FIG. 18). The counterclockwise rotation of the pivotal member 18 counterclockwise rotates the lower hook 42, thereby unlocking the front sliding sleeve 2 (see FIG. 19). The auxiliary spring 40 then expands to push the rear sliding sleeve 4 rearward. The main tube 5 moves rearward to compress the cup member 71 until the flange 52 contacts the limit member 71 and the inlet 51 communicates with the air chamber 13 (see FIG. 20). Pressurized gas from an air canister (not shown) flows to the air chamber 13 and in turn flows through the main tube 5 via the inlet 51. And in turn, the gas flows through the gas piston 54 to discharge the pellet 53 out of the barrel 50 to fire. At the same time, a portion of the gas flows into the diversion channel 22 to push the front sliding sleeve 2 rearward by compressing the auxiliary spring 40 and expanding the main spring 20 (see FIGS. 19, 20 and 21). And in turn, the gas piston 54 moves rearward to unblock the top opening of the column 61, resulting in a new pellet 53 being pushed upward into the receptacle 12 to be ready for a next firing. Gas is stopped from supplying to the air chamber 13. The cup member 71 is pushed forward due to the expansion of the elastic component thereof. The flow path from the air chamber 13 to main tube 5 via the inlet 51 is blocked due to the disengagement the inlet 51 from the air chamber 13. Further, the upper hook 41 lockingly engages the upper recess 23 and the lower hook 42 lockingly engages the lower recess 24. This loading of pellet is automatic. Next, as shown in FIG. 22, the compression of the main spring 20 and the compression of the auxiliary spring 40 pushes the rear sliding sleeve 4 forward. And in turn, the upper hook 41 is pressed by the roller 21 in the forward movement of the rear sliding sleeve 4, thereby disengaging the front end of the upper hook 41 from the upper recess 23. Also, the pivotal member 18 pivotably pushes the rear portion of the lower hook 41 upward to disengage the front end of the lower hook 42 from the lower recess 24. The auxiliary spring 40 then expands to push the rear sliding sleeve 4 rearward. The main tube 5 moves rearward to compress the cup member 71 until the flange 52 contacts the limit member 71 and the inlet 51 communicates with the air chamber 13 (see FIG. 23). Pressurized gas from an air canister (not shown) flows to the air chamber 13 and in turn flows through the main tube 5 via the inlet 51. And in turn, the gas flows through the gas piston 54 to discharge the pellet 53 out of the barrel 50 to fire. At the same time, a portion of the gas flows into the diversion channel 22 to push the front sliding sleeve 2 rearward by compressing the auxiliary spring 40 and expanding the main spring 20 (see FIGS. 23, 24 and 25). And in turn, the gas piston 54 moves rearward to unblock the top opening of the column 61, resulting in a new pellet 53 being pushed upward into the receptacle 12 to be ready for a next firing. Gas is stopped from supplying to the air chamber 13. The cup member 71 is pushed forward due to the expansion of the elastic component thereof. The flow path from the air chamber 13 to main tube 5 via the inlet 51 is blocked due to the disengagement the inlet 51 from the air chamber 13. Further, the upper hook 41 lockingly engages the upper recess 23 and the lower hook 42 lockingly engages the lower recess 24. The main spring 20 is expanded and the auxiliary spring 40 is compressed. This loading of pellet is automatic. Next, as shown in FIG. 25, the user may pull the trigger 16 but the pivotal member 18 does not pivot. A releasing of the trigger 16 disengages the pivotal member 18 from the front stop member 32 due to expansion of the rear spring 19 (see FIG. 26). Finally, both the front sliding sleeve 2 and the rear sliding sleeve 4 move forward to a ready to fire position of the automatic firing mode (see FIG. 27).

While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims.

Claims

1. An automatic air rifle capable of automatic and semiautomatic fire comprising: a receiver;a hollow limit member secured to a rear portion of the receiver;a spring-actuated cup member disposed in the limit member;an elongated cavity disposed in the receiver;a receptacle disposed at a front end of the cavity;an air chamber disposed at a rear end of the cavity;a fire control selector rotatably mounted on the receiver, the fire control selector being configured to rotate to point to a safe position, a semi-automatic position, or a fully automatic position;a cam member disposed in the receiver and co-rotated with the fire control selector;a first spring-biased member disposed to the left of the cam member;a second spring-biased member disposed to the right of the cam member;a spring-biased trigger pivotably secured to the receiver;a spring-biased pivotal member partially disposed in the trigger;a charging handle retractably disposed in the receiver;a front sliding sleeve disposed in a forward portion of the cavity and including an upper recess at a rear end and a lower recess under the upper recess;a main biasing member secured to the front sliding sleeve and the charging handle respectively;a roller rotatably disposed in the cavity;an L-shaped rod disposed in the cavity;a rear stop member disposed at an end of a short part of the L-shaped rod and between the cam member and the second spring-biased member;a front stop member disposed at an end of a long part of the L-shaped rod;a rear diversion channel formed through the front sliding sleeve;a rear sliding sleeve disposed rearward of the front sliding sleeve and including a spring-biased, pivotal upper hook and a spring-biased, pivotal lower hook;a main tube disposed through the rear sliding sleeve and having a rear end slidably disposed in the cup member, and a front end fastened in the front sliding sleeve, the main tube including a rear inlet and an annular flange disposed forwardly of the rear inlet;a gas piston disposed forwardly of the main tube and partially in the front sliding sleeve, the gas piston having a front end disposed in the receptacle;a magazine releasably secured to the receiver and including a column for storing at least one pellet wherein one of the at least one pellet is pushed to contact an outer surface of the front end of the gas piston;a barrel having a rear end communicating with the front end of the gas piston;an inlet member formed at a rear end of the gas piston; andan auxiliary biasing member put on the main tube and biased between the front sliding sleeve and the rear sliding sleeve;wherein in response to rotating the fire control selector to the semi-automatic position, the cam member is disposed perpendicular to both the first and second spring-biased members, the rear stop member is not urged by the cam member, a pulling of the charging handle pulls the front sliding sleeve to be proximate the main tube, the gas piston moves rearward to allow one of the at least one pellet to enter the receptacle, the main biasing member expands, the upper hook lockingly engages the upper recess, the lower hook lockingly engages the lower recess, the auxiliary biasing member compresses, a releasing of the charging handle compresses the main biasing member to push both the front and rear sliding sleeves forward, the gas piston moves forward to push one of the at least one pellet into a rear end of the barrel, the upper hook is pressed by the roller in the forward movement of the rear sliding sleeve to disengage from the upper recess, a pulling of the trigger counterclockwise rotates both the pivotal member and the lower hook to unlock the front sliding sleeve, the auxiliary biasing member expands to push the rear sliding sleeve rearward, the main tube moves rearward to compress the cup member until the flange contacts the limit member and the rear inlet communicates with the air chamber, pressurized gas flows through the barrel via the air chamber, the rear inlet, the main tube, and the gas piston to discharge one of the at least one pellet out of the barrel, a portion of the pressurized gas flows into the diversion channel to push the front sliding sleeve rearward by compressing the auxiliary biasing member and expanding the main biasing member, the gas piston moves rearward to allow a next one of the at least one pellet to enter the receptacle, a stop of flowing the pressurized gas pushes the cup member forward to disengage the rear inlet from the air chamber, the upper hook lockingly engages the upper recess, the lower hook lockingly engages the lower recess, a pulling of the trigger counterclockwise rotates the pivotal member and moves the pivotal member along an outer surface of the lower hook without counterclockwise rotating the lower hook, the main biasing member compresses to push the rear sliding sleeve forward and compress the auxiliary biasing member, the upper hook is pressed by the roller in the forward movement of the rear sliding sleeve to disengage from the upper recess, and a release of the trigger clockwise rotates the pivotal member to disengage from the lower hook to dispose the trigger in a ready position; andwherein in response to rotating the fire control selector to the fully automatic position, the cam member is disposed perpendicular to both the first and second spring-biased members, the rear stop member is not urged by the cam member, a pulling of the charging handle pulls the front sliding sleeve to be proximate the main tube, the gas piston moves rearward to allow one of the at least one pellet to enter the receptacle, the main biasing member expands, the upper hook lockingly engages the upper recess, the lower hook lockingly engages the lower recess, the auxiliary biasing member compresses, a releasing of the charging handle compresses the main biasing member to push both the front and rear sliding sleeves forward, the gas piston moves forward to push one of the at least one pellet into a rear end of the barrel, the upper hook is pressed by the roller in the forward movement of the rear sliding sleeve to disengage from the upper recess, a pulling of the trigger counterclockwise rotates both the pivotal member and the lower hook to unlock the front sliding sleeve, the auxiliary biasing member expands to push the rear sliding sleeve rearward, the main tube moves rearward to compress the cup member until the flange contacts the limit member and the rear inlet communicates with the air chamber, first pressurized gas flows through the barrel via the air chamber, the rear inlet, the main tube, and the gas piston to discharge one of the at least one pellet out of the barrel, a portion of the first pressurized gas flows into the diversion channel to push the front sliding sleeve rearward by compressing the auxiliary biasing member and expanding the main biasing member, the gas piston moves rearward to allow a next one of the at least one pellet to enter the receptacle, a stop of flowing the first pressurized gas pushes the cup member forward to disengage the rear inlet from the air chamber, the upper hook lockingly engages the upper recess, the lower hook lockingly engages the lower recess, the main biasing member compresses, the auxiliary biasing member compresses to push the rear sliding sleeve forward, the upper hook is pressed by the roller in the forward movement of the rear sliding sleeve to disengage from the upper recess, a pulling of the trigger counterclockwise rotates both the pivotal member and the lower hook to unlock the front sliding sleeve, the auxiliary biasing member expands to push the rear sliding sleeve forward, the upper hook is pressed by the roller in the forward movement of the rear sliding sleeve to disengage from the upper recess, the pivotal member pivotably pushes the lower hook to disengage from the lower recess, the auxiliary biasing member expands to push the rear sliding sleeve rearward, the main tube moves rearward to compress the cup member until the flange contacts the limit member and the rear inlet communicates with the air chamber, second pressurized gas flows through the barrel via the air chamber, the rear inlet, the main tube, and the gas piston to discharge one of the at least one pellet out of the barrel, a portion of the second pressurized gas flows into the diversion channel to push the front sliding sleeve rearward by compressing the auxiliary biasing member and expanding the main biasing member, the gas piston moves rearward to allow a next one of the at least one pellet to enter the receptacle, a stop of flowing the second pressurized gas pushes the cup member forward to disengage the rear inlet from the air chamber, the upper hook lockingly engages the upper recess, the lower hook lockingly engages the lower recess, the main biasing member, the main biasing member expands, the auxiliary biasing member compresses, and both the front and rear sliding sleeves move forward to dispose the trigger in the ready position.