Note: Descriptions are shown in the official language in which they were submitted.
CA 02756606 2011-11-01
PNEUMATICALLY POWERED PROJECTILE LAUNCHER OR AIR GUN
FIELD OF THE INVENTION
The present invention relates generally to pneumatically powered projectile
launchers or air guns, and more particularly to a pneumatic launcher or air
gun
configured to use relatively large projectiles for high muzzle energy at
relatively low
muzzle velocity.
BACKGROUND OF THE INVENTION
In some other countries, use of firearms for self defense is permissible. In
Canada however, the laws are such that you cannot have a firearm stored in a
readily accessible manner useful for such purposes.
The definition of a firearm, according to the RCMP is as follows:
"A firearm is a barrelled weapon from which any shot, bullet or other
projectile can be discharged and that is capable of causing serious
bodily injury or death to a person, and includes any frame or receiver
of such a barrelled weapon, as well as anything that can be adapted
for use as a firearm."
(Source: http://www.rcmp-gre.gc.ca/cfp-pcaf/faq/index-eng.htm).
Exceptions to this definition include some air guns, with certain performance
characteristics and the manner of use of the air gun being used to determine
whether they qualify as firearms, as follows:
Air guns that are firearms for purposes of both the Firearms Act
and the Criminal Code.
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"These are air guns with both a high muzzle velocity (greater than 2
152.4 meters or 500 feet per second) and a high muzzle energy
(greater than 5.7 joules or 4.2 foot-pounds). The "muzzle velocity" is
the speed of a projectile at the instant it leaves the muzzle of a gun,
normally expressed in metres per second or feet per second. The
"muzzle energy" is the energy of a projectile at the instant it /eaves the
muzzle of a gun, expressed in joules or foot-pounds. Air guns need to
meet both standards to be classified as firearms for purposes of the
Firearms Act.
Air guns that meet the Criminal Code definition of a firearm, but
that are deemed not to be firearms for certain purposes of the
Firearms Act and Criminal Code.
These are air guns with a maximum muzzle velocity of 152.4 meters or
500 feet per second and/or a maximum muzzle energy of 5.7 joules or
42 foot pounds.
Such air guns are exempt from licensing, registration, and other
requirements under the Firearms Act, and from penalties set out in the
Criminal Code for possessing a firearm without a valid licence or
registration certificate. However, they are considered to be firearms
under the Criminal Code if they are used to commit a crime. Anyone
who uses such an air gun to commit a crime faces the same penalties
as someone who uses a regular firearm.
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The simple possession, acquisition and use of these air guns for lawful
purposes is regulated more by provincial and municipal laws and by-
laws than by federal law. For example, some provinces may have set a
minimum age for acquiring such an air gun. For more information,
please contact your local or provincial authorities.
These air guns are exempt from the specific safe storage,
transportation and handling requirements set out in the regulations
supporting the Firearms Act. However, the Criminal Code requires that
reasonable precautions be taken to use, carry, handle, store, transport,
and shipped them in a safe and secure manner.
(Source: http://www.rcmp-grc.gc.ca/cfp-pcaf/fs-fd/air gun-arme_air-eng.htm).
Accordingly, having air guns with a muzzle velocity of less than 500 feet per
second and/or a muzzle energy of 4.2 foot-pounds or less are not considered
firearms for the purposes of the Firearms Act and the Criminal Code, so long
as they
are not used to commit a crime.
This has led the applicant to create a personal protection device that meets
the performance criteria for being an airgun without qualification as a
firearm,
preferably with a muzzle velocity below 500 fps (feet per second) but using
HPA
(high pressure air) to provide sufficient muzzle energy for ample stopping
power
against an attacker. As a non-firearm, the air gun would thus be excluded from
the
specific safe storage, transportation and handling requirements set out in the
regulations supporting the Firearms Act, in which case storage in a ready-to-
defend
CA 02756606 2011-11-01
manner would not be an offence under that act, which requires that firearms be
4
stored in unloaded condition and locked away or rendered inoperable.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which illustrate an exemplary embodiment of
the present invention:
Figure 1 is a side elevational view of an air gun according to the present
invention.
Figure 2 is a partial cross-sectional view of the air gun of Figure 1 as a
first
ball-shaped projectile is propelled through the barrel and the bolt returns to
its
default position allowing automatic loading of a second ball-shaped projectile
from a
magazine.
Figure 3 is a partial cross-sectional view of the air gun, with biasing
springs
omitted for ease of illustration, before the trigger is depressed to advance
the bolt
from its default position and propel the first projectile of Figure 2 down the
barrel.
Figure 4 is a partial cross-sectional view of the air gun, with the biasing
springs again omitted for ease of illustration, as the first projectile of
Figure 3 is
propelled down the barrel from the advanced bolt, which temporarily blocks the
loading of the second projectile from the magazine.
Figure 5 is a partial cross-sectional view of the air gun showing the
condition
of the trigger assembly when the air gun is in a ready to fire condition with
a fully
pressurized dump tank.
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Figure 6 is a partial cross-sectional view of the air gun as the trigger is
initially
depressed from the ready to fire condition of Figure 5 to withdraw a stop
member or
bolt catch from the bolt.
Figure 7 is a partial cross-sectional view of the air gun as the trigger
remains
in the depressed condition of Figure 6 and the bolt is driven forward by air
from the
dump tank and the stop member is forced out of engagement with the trigger by
a
spring.
Figure 8 is a partial cross-sectional view of the air gun as the trigger
remains
in the depressed condition of Figure 7 and the bolt has been spring-returned
to its
default retracted position, where it is engaged by the stop member to maintain
this
position until a subsequent pulling of the trigger with the dump chamber
pressurized.
DETAILED DESCRIPTION
Structure
Figure 1 shows an air gun 10 of the present invention, featuring a barrel 12
having a muzzle end 14 and an opposing breech end 16, a receiver 18 disposed
at
the breech end 16 of the barrel, a dump chamber 20 containing a rear end of
the
receiver 18 opposite the barrel 12, a hand grip 22 depending downward from the
underside of the dump chamber 20, a magazine 24 releasably attached to and
depending downward from the underside of the barrel 12 at the breech end 16
thereof, a trigger assembly 26 attached to the underside of the receiver 18
and
presenting a trigger 28 depending downwardly away therefrom in front of the
hand
grip 22, and a high pressure air (H PA) tank 30 attached at the bottom of the
hand
grip.
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Turning to Figure 2, a hollow bolt 32 has a larger outer diameter cylindrical
6
portion 34 residing within a cylindrical interior bore of the receiver 18 and
a smaller
outer diameter cylindrical portion 36 extending from the larger diameter
portion 34
partially into the barrel 12 through the breach end 16 thereof. The hollow
bolt
features an axial through-bore 32a running through it, from its larger
diameter rear
end 34a nearest a closed rear wall 38 of the receiver to its opposing smaller
diameter front end 36a in the breech of the barrel 12. The bore 32a of the
bolt is
cylindrical from the bolt's rear end 34a to near the bolt's front end 36a,
where the
bore then flares smoothly outward to the front end of the bolt. A compression
spring
40 coils around the smaller diameter portion 36 of the bolt 32 between the
breech
end 16 of the barrel 12, which is located a short distance inside the front
end of the
receiver, and the shoulder defined on the exterior of the bolt at the
transition
between the large and small diameter portions 34, 36, thereby biasing the bolt
32
toward the closed rear wall 38 of the receiver 18.
Just outside the front of the receiver 18, a cylindrical collar 42 depends
perpendicularly downward from the underside of the barrel in a manner
encircling a
hole or opening 44 therein in order to concentrically receive the upper
portion of the
tubular body 46 of the magazine 24 to position the open upper end of the
magazine
tube 46 adjacent the opening 44 in the barrel. Mechanisms for securing a
magazine
in this received position nested inside the magazine collar 42 of the barrel
are
known, and thus not shown or described herein. Inside the magazine, a coiled
compression spring 48 is disposed between the closed bottom 50 of the magazine
tube 46 and a plurality of solid metal-balls stacked atop the spring, thus
forcing the
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uppermost one of the balls into the barrel 12 adjacent the breech end thereof.
Figure 2 shows the magazine in a nearly consumed condition, having only one
metal
ball 52 remaining therein. In addition to storing the round-ball projectiles,
the
magazine also doubles as a fore grip for additional support of the air gun by
the
operator's second had at a distance ahead of the main hand grip 22.
The dump chamber 20 has its front end fixed to the receiver 18 in a manner
sealed therearound at an axially intermediate therealong to enclose a rear
portion of
the receiver within the hollow interior of the dump chamber 20. This rear
portion of
the receiver includes the closed rear wall 38 and a series of circumferential
ports or
openings 54 (Fig. 4) located in the peripheral wall of the receiver 18 a short
distance
ahead of the closed rear wall 38 to allow fluid communication between the
interior
space of the receiver 18 and the dump tank interior 56 containing the rear
portion of
the receiver. Except for these openable and closable ports 54, the interior of
the
receiver is otherwise sealed off from the interior of the dump chamber 20.
An axial bore through the closed end 38 of the receiver 18 slidably supports
and seals with an intermediate portion of a plunger 58 having an enlarged head
or
stop 60 at is rear end, and similar stop or flange 62 near its front end. The
rear end
stop 60 of the plunger 58 resides in the outside the receiver 18 in the
interior 56 of
the dump chamber 20. When the plunger 58 slides toward a forwardmost position,
=
limited by contact of the rear stop 60 against the outside the receiver's
closed rear
wall 38, the front end 62 of the plunger passes by the rearmost extent of the
ports
54. In the opposite direction, the plunger 58 can slide into a rearmost
position in
which the stop 62 at the front end of the plunger 58 becomes seated in a
recess 64
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provided in the otherwise-flat inner surface of the receiver's closed rear
wall 38 by a 8
counterbored end of the plunger-receiving bore. Contact of the shoulder
defined
between the front stop 62 of the plunger and the smaller-diameter intermediate
portion of the plunger 58 with the corresponding shoulder defined by the inner
end of
the counter-bore 64 defines the rearmost position of the plunger, where the
front
stop 62 is at least partially recessed in this counterbore 64 to minimize or
avoid any
extension of the plunger 58 into the interior space of the receiver. Figure 3
shows
the plunger 58 in its rearmost position, and Figure 4 shows it in its
forwardmost
position.
An inlet valve 66 located at the rear of the dump chamber 20 features a
hollow cylinder 68 having a first open end 70 open to the exterior of the dump
chamber 20 at the rear wall thereof, an opposing closed end 72, and a series
of
circumferential ports or openings 74 extending radially through the peripheral
wall of
the cylinder adjacent the closed end wall 72 thereof. Opening and closing of
the
valve 66 is achieved by a cylindrical sleeve 76 slidably disposed around the
exterior
of the cylinder 68. The cylinder 68 extends into an open end of the sleeve 76
toward
an opposing closed end 78 thereof. The sleeve 76 features a series of
circumferential ports or holes 80 extending radially through the peripheral
wall of the
sleeve 76 near the closed end wall 78 thereof. The outer end of the cylinder
68
located at the rear wall of the dump chamber 20 is adapted in a conventional
manner for coupling to the outlet valve of a high pressure air tank so that
the tank
feeds into the internal bore of channel of the cylinder. In the illustrated
embodiment,
the tank is connected at the bottom of the grip, and thus is routed to the
dump
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9
chamber via internal or external hose or piping (not shown). Alternatively,
the HPA
tank could be attached at the back of the dump chamber. The illustrated
position
may be optimal, as the end of the tank can be used as a buttstock and placed
against the shoulder, aligning the barrel fairly close to the user's sight
line. Also
having the tank behind the hand grip may help balance the device.
Sliding seals (not shown) are provided around the periphery of the cylinder on
opposing sides of the ports 74 therein to seal against the surrounding inner
peripheral surface of the sleeve 78 while allowing sliding between the two
components. Thus, when the closed end of the cylinder resides between the
sleeve
ports 80 and the closed end 78 of the sleeve 76 (as shown in Fig. 3), the
ports of the
two pieces are in fluid communication, thereby opening the valve in order to
fluidly
communicate the bore of the cylinder 68 with the surrounding interior of the
dump
chamber. When the closed end of the cylinder is located on the side of the
sleeve
ports 80 opposite the closed end of the sleeve 78 (as shown in Fig. 4), the
valve is
closed, sealing off the cylinder, and the pressurized air tank coupled
therewith, from
the dump chamber interior. With reference to Figure 2, a compression spring 82
disposed between the open end of the sleeve 76 and the rear wall of the dump
chamber biases the sleeve into the valve-closing position.
The trigger assembly features a first pin 84 on which the trigger 28, and an
extension 86 defined integrally therewith as part of a same unitary body, are
pivotally
carried for rotation about an axis perpendicular to the barrel axis along
which the bolt
32 is slides in the receiver and breech end of the barrel. The extension 86
extends
forwardly from the first pin 84, while the trigger 28 depends downwardly from
the first
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pin 84 to extend outward from a housing 88 of the trigger assembly, on which
the
first 84 pin is supported at a side wall of the housing 88. A compression
spring 90 is
disposed between a bottom of the trigger extension 86 and a bottom wall of the
trigger housing 88 to force the extension upward, and thereby bias the trigger
28
forward into its normal default position. A slide member 92 is slidably
disposed
within a slot or channel extending along the trigger extension 86 from the
front end
thereof. A compression spring 94 disposed between the slide member 92 and the
closed end of the slot or channel furthest from the front end of the trigger
extension
in order to bias the front end of the slide member to a position jutting past
the front
end of the extension. The travel of the slide member in this direction is
limited by
cooperation of a pin 96 jutting from a side of the slot or channel of the
trigger
extension with a slot 98 in the slide member. The slide member 92 cooperates
with
a stop member 100 of the trigger assembly to move the stop member out of a
position engaging against the bolt 32 when the trigger is depressed toward the
hand
grip 22.
The stop member 100 is an elongated piece having a lower end disposed
within the housing 88 of the trigger assembly 26 in front of the trigger
extension 86
and an upper end reaching into the receiver 18 via a hole in the bottom
thereof and
a notch 102 aligned with that hole in the bottom of the barrel 12 at the
breech end 16
thereof. A cross-pin 104 in the hole in the bottom of the receiver pivotally
supports
the stop member 100 for rotation about an axis parallel to the pivot axis of
the trigger
28, and the opening 105 in the stop member through which the cross-pin 104
extends is elongated in the longitudinal direction of the stop member to allow
limited
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sliding thereof up and down on the cross-pin 104 to change how far the stop
member projects upward into the receiver 18. The bottom end of the stop member
100 features a catch 106 that presents an upward facing ledge or shoulder
jutting
toward the pivot pin 84 of the trigger. A compression spring 108 disposed
between
the bottom wall of the trigger assembly housing 88 and the lower end of the
stop
member 100 acts upward and forward thereon, tending to slide the stop member
upward on the cross-pin 84 and pivot the bottom end of the stop member forward
about the cross-pin 86. A recess or notch 110 in the underside of the bolt 32
hear
the front end 36a thereof receives the top end of the stop member 100 when the
stop member is biased into its uppermost position in the receiver 18 and the
bolt 32
is biased into its rearmost position nearest the closed rear wall of the
receiver, which
places the recess 110 over the notch 102 at the breech end 16 of the barrel
12.
Operation
Having described the structure of the air gun, its operation will now be
described.
Coil spring 40 biases the bolt 32 into a rearward position near the closed
rear
end 38 of the receiver. With the bolt in this position, a pair of
circumferential seals
(not shown) are engaged between the large diameter portion 34 of the bolt 32
and
the surrounding inner peripheral wall of the receiver on opposite sides of the
ports
54 in this wall of the receiver, thereby sealing off the receiver interior
from the dump
chamber 20. The seals are located on the bolt, so as to slide along the
receiver
during movement of the bolt. This rearward position of the bolt defines a
loading
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position, as the front end 36a of the bolt 32 is situated just behind the
opening 44 12
through which metal balls are fed into the barrel by the magazine. With the
trigger
28 and the stop member 100 biased into their default positions by the
respective coil
springs 90, 108, as shown in Figure 5, the top end of the stop member 100
projects
into the recess 110 in the underside of the bolt 32, and the catch 106 at the
bottom
of the stop member catches under the forwardmost end of the slide member 92
exposed at the front of the trigger extension 86. The top end of the stop
member
abuts against the end of the bolt recess 110 nearest the larger diameter rear
end
34a of the bolt, thereby blocking pivotal movement of the stop member 100 on
the
cross-pin 104 in the direction that would pull the catch 106 forwardly out
from under
the slide member 92 of the trigger extension 86. The raised position of the
stop
member 100 to engage into the recess 110 in the exterior of the bolt prevents
any
forward movement of the bolt 32. The forcing of the bolt 32 into its rearward
position
by the respective spring 40 causes the rear end 34a of the bolt 32 to push
reward on
the plunger 58, which in turn is long enough to push rearward on the closure
sleeve
78 of the inlet valve against the spring 82 pushing forward thereagainst. The
bolt
spring 40 is stronger than the valve spring 82, and so this biasing of the
bolt into the
rearward loading position overcomes the bias of the valve spring 82 to move
the
valve closure sleeve 76 into the open position allowing airflow into the dump
chamber.
With the HPA tank 30 connected, high pressure thus air flows into the dump
chamber 20 through the inlet valve 66 contained inside the dump chamber, which
may be regulated in a known manner to fill to a predetermined pressure. Once
the
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13
pressure inside the dump chamber 20 reaches the predetermined value, the
device
is ready to fire the metal ball that has been automatically loaded into the
barrel in
front of the bolt by the magazine. When the trigger 28 is pulled rearward from
the
ready to fire condition of Figure 5, the catch 106 of the stop member 100 is
pulled
downward by the slide member 92 of the trigger extension 86 under the pivoting
of
the trigger and extension about the respective pin 84, thereby withdrawing the
top
end of the stop member 100 from the recess 110 of the bolt and thus unlocking
the
bolt from its rearward loading position, as shown in Figure 6. Initially the
bolt is held
in this rearward loading position by the respective spring 40. However, the
high
pressure air in the dump tank acts on the rear end of the plunger 58, pushing
the
plunger 58 forward in the dump tank. To cause this desired directional
movement of
the plunger 58, the rear end 58a of the plunger has a reduced diameter smaller
than
both the rear stop 60 located adjacent that end, and the intermediate portion
of the
plunger between the two stops 60, 62. This way, there is a greater surface
area for
the dump tank pressure to act against in the forward direction at the rear
face of the
rear stop 60 than in the rearward direction at the front face of the rear
stop. The
extension of this reduced-diameter rear end of the plunger past the rear stop
60
creates a space in which the dump chamber air pressure can act between the
plungers rear stop 60 and the closed end 78 of the inlet valve sleeve 76.
The inlet valve sleeve 76 follows the plunger 58 under the action of the
respective spring 82, so that under sufficient forward travel of the plunger
58, the
sleeve moves into the closed position turning off the inlet valve 66, thereby
cutting
off the supply of high pressure air to the dump chamber from the HPA tank 30.
The
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forward motion of the plunger 68 also pushes the bolt 32 forward in the
receiver 18,
so that simultaneous to, or just after, this shutting off of the inlet valve,
the rear end
of the bolt reaches the ports 54 in the receiver's peripheral wall, opening
the ports as
the seal near the rear end of the bolt moves past the rearmost extent of the
ports.
This opening of these ports or vent holes in the receiver wall allows the HPA
contained in the dump chamber to rapidly expand through these vent holes, into
the
receiver, forcing the bolt to the fully forward position, and flowing through
the axial
bore in the middle of the bolt into the barrel, pushing the ball-shaped
projectile out of
the barrel at the muzzle. When in its rearward loading position, the front end
of the
bolt resides immediately behind the location where the magazine opens to the
barrel, and so the initial movement of the bolt under the action of the
plunger
immediately begins to close off the magazine opening to the barrel above, and
so
the subsequent movement of the bolt under the introduction of the high
pressure air
to the receiver quickly completes this closure of the magazine in an
effectively
instantaneous manner to close of the magazine before any high pressure air can
gain entry thereto. Circumferential seals (not shown) on the interior wall of
the barrel
on opposite sides of the magazine opening provide an air tight fit between the
bolt
and the barrel.
As described above, the stop member is spring loaded for two types of biased
motion, a rotational motion and an upward sliding motion. Once it has been
pulled
downward by the trigger far enough to release the bolt, as shown in Figure 6,
the
stop member will rotate (clockwise in Figs. 3 & 4, counterclockwise in Figs.
2, 5 & 6)
and disengage its catch 106 from under the slide member 92 of the trigger
extension
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15
86, as shown in Figure 7. Once it has disconnected from the trigger assembly,
the
stop member will be forced upward against the bolt, awaiting return of the
bolt to its
rearward position under the action of the bolt spring 40, where the stop
member will
then again align with the recess 110 in the underside of the bolt and lock
into place
in this recess to once again secure the bolt in the loading position, as shown
in
figure 8. The disconnecting of the stop member catch from the trigger makes
the air
gun operate in only a semi automatic mode of fire, as the trigger can remain
depressed rearward after firing, and the stop member will nonetheless still
stop the
bolt from proceeding forward, as demonstrated in Figures 5-8. Once the trigger
has
been released, it will reconnect with the catch of the stop member, allowing
for the
device to be shot again with another depression of the trigger.
With reference to Figures 5 and 8, should the trigger only be released from
the depressed condition of Figure 8 after the stop member 100 has returned to
it's
ready to fire position of engaged against the rear end of the bolt notch 110
as shown
in Figure 5, the slide member 92 of the trigger will retract further into the
trigger
extension under contact of the slide with the stop member, which is clamped in
place
between the rear end of the bolt notch 110 and the front end of the barrel
notch 102,
while the front end of the trigger extension is raised under the return action
of spring
90, thereby preventing the trigger extension from catching on the underside of
the
stop member 100. To ensure this a smooth trouble-free return of the trigger to
its
normal position, the front end of the slide 92 and the rear-bottom end of the
stop
member catch 106 are obliquely angled with a same forward and downward
direction of slope so that under upward movement of the slide 92 with the
trigger
CA 02756606 2011-11-01
16
extension about pin 84, the slide's sloped forward end will slidingly
interface with the
sloped rear-bottom corner of the stop member catch 106, forcing the slide 92
back
into the trigger extension 86 against spring 94 so as to clear the stop member
catch
106 to allow return of the trigger to its normal default position. Once the
slide has
cleared the stop member catch 106, spring 94 returns the slide to its
defaulted
extended position, as defined by abutment of the rear end of slot 98 against
pin 96
to once extend the front end of the slide 92 far enough forward to engage over
the
stop member catch 106.
Once the pressure inside the device has lowered, the spring loaded bolt starts
travelling rearward, allowing another projectile from the magazine to load
into the
barrel, re-sealing the receiver from the dump chamber by closing the vent
holes or
ports of the receiver, and restarting the flow of HPA into the dump chamber
from the
HPA tank by pushing the plunger 58, and in turn the valve sleeve 76, rearward
against the valve spring 82 to reopen the inlet valve 66. When the bolt has
moved all
the way rearward, the stop member 100 will lock the bolt 32 in its rearward
position.
Once the dump chamber is again pressurized to the predetermined level, the
device
is ready to be fired again.
Performance
To obtain a suitable balance between desired high-level muzzle energy and
low enough muzzle velocity to avoid classification as a firearm under current
Canadian legislation, one embodiment employs a 4500 psi HPA tank, a regulated
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dump chamber pressure of 2000 psi, an internal barrel diameter and a
projectile
diameter of approximately 1-inch, a 0.75-inch bore through the bolt.
Commercially available Portable HPA tanks come in many different
capacities, including a range from 13 cubic inches to 110 cubic inches, and
many
different pressures, including a range from 3000 to 5000 PSI. The selection of
4500
PSI for the aforementioned embodiment is based on limited availability and
high cost
of higher pressure 5000 PSI tanks. The capacity of the tank could be any of
the
available sizes, for example depending on the preference of the end user.
Alternatively, specialized tanks of shape, size or dimension varying from
existing
commercially available units may of course be used.
A 68 cubic inch tank at 4500 PSI for example contains -20750 cubic inches of
air at normal atmospheric pressure. For the example of a 1 inch diameter
projectile,
with a 6 inch barrel, a calculated average pressure needs to be -1500 PSI, to
reach
421 fps with a muzzle energy of 589 foot pounds. For the embodiment employing
the values listed above, the starting pressure would be 2000 PSI at the breech
of the
barrel, and 1000 Psi at the muzzle of the barrel, giving a 1500 PSI average
down the
length of the barrel. A tank of this pressure would need to be regulated for
different
models of the air gun or Personal Protection Device, to achieve consistent
muzzle
velocities independent of barrel diameter or length. That is, for shorter
barreled
models, the pressure contained within the dump chamber would need to be higher
to
achieve the same velocity as a longer barreled model with a lower pressure.
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18
Based on the initial calculations, a tank size of 68 cubic inches 4500 PSI
would get approximately 26 full power shots out of a model built to the
specifications
listed as the first example in the table below.
Diameter
Barrel Projectile Velocity
Muzzle Energy
(inch) Av PSI g. Length
Weight (kg) (fps)
(foot lbs)
(inch)
1 1500 6
0.097 421.0081
589.0486
1 1800 5
0.097 421.0081
589.0486
1 2250 4
0.097 421.0081
589.0486
1 3000 3
0.097 421.0081
589.0486
0.75 1135 6
0.041 422.472
250.7138
0.75 1360 5
0.041 422.1617
250.3457
0.75 1700 4
0.041 422.1617
250.3457
0.75 2275 3
0.041 422.937
251.2661
0.5 750 6
0.0121 421.4428
73.63108
0.5 900 5
0.0121 421.4428
73.63108
0.5 1125 4
0.0121 421.4428
73.63108
0.5 1500 3
0.0121 421.4428
73.63108
The calculations used the projectile/barrel diameter, associated projectile
weight for a preselected projectile material (e.g. lead), barrel length, and
average
barrel pressure as input values, from which the muzzle velocity and energy
could be
calculated. For the different projectile sizes and barrel lengths,
calculations were
repeated for various pressure values to find pressures suitable to achieve a
muzzle
velocity approaching, but less than, 500 feet per second. Selecting an
approximate
muzzle velocity of 420 feet per second as a desirable target, leaving a margin
of 80
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19
feet per second, led to the optimal values charted herein above. The charted
calculation results of pressures required for different diameters and lengths
of
barrels demonstrate a preference for a 1-inch projectile based on the expected
stopping power based on the calculated muzzle energy.
The 0.5" lead sphere at 421 FPS provides 73.6 ft/lbs of energy, while a 1.5"
lead sphere at 421 FPS provides 1992 ft/lbs of energy. Preferred embodiments
would provide at least 662 ft/lbs of energy/square inch of the projectiles
largest
cross-sectional area (in planes normal to the barrel axis) and greater. The 1"
lead
sphere with 589 ft/lbs of energy is equal to 755 ft/lbs per square inch, and
should
penetrate 14.25 inches of ballistic gelatin. This is just better than the 12.5-
14 inches
of penetration recommended by defensive experts. The 0.75" inner barrel
diameter
model with 250ft/lbs of energy, equal to 568ft/lbs per square inch, should
penetrate
10.72 inches of ballistic gelatin. The .5" ID model with 73.6 foot pounds
equal to 375
ft/lbs per square inch should penetrate 7.09 inches of ballistics gel.
Based on the above achievable energy values, 0.5" is the preferred minimum
projectile size. Preferred embodiments would not exceed a projectile diameter
of
1.5" to avoid excessive weight issues. Six 1.5" diameter lead spheres will
still weigh
1.968 KG, with the larger device's weight on top of that. Six 1.75" diameter
lead
spheres would weigh 3.126 KG, six 2" lead spheres would weigh 4.668 KG.
Estimations suggest that the embodiment with the 6" long barrel with 1"
internal
diameter barrel, fully loaded, would be almost 6 pounds. If the 1.5" internal
diameter
device would be 25% heavier, with the six 1,5" lead spheres it would be just
over 10
CA 02756606 2011-11-01
20
pounds. If the 2" internal diameter device would be 50% heavier with six 2"
lead
spheres, it would weigh almost 17.25 pounds.
It will be appreciated that aspects of the air gun design disclosed herein can
also be employed to provide results other than the under 500-fps performance
described above, for example in producing an air gun design that doesn't
qualify as
an exemption to the firearm definition reference in the background.
Accordingly, a
wide variety of supply pressures, dump chamber pressures, projectile sizes and
shapes may be used while still employing unique aspects of the design falling
within
the scope of the present invention. For example, versions lacking semi-
automatic
capabilities or magazine-carried projectiles may nonetheless employ the unique
arrangement of a plunger used to initiate the firing process by displacing the
bolt to
open communication ports between the receiver and a pressurized dump chamber.
While the preferred embodiment features solid spherical projectiles fired one
at a
time to provide relatively stable short-distance flight without a rifled
barrel, it may be
possible to use shot, in combination with a wad or shot cup, or non-spherical
single
projectiles such as slugs of more elongated shape, for example of slug shape
similar
to pellets for a pellet rifle, with a heavy front end and skirted rear end,
like a
badminton birdie. However, the spherical projectiles of the illustrated
embodiment
avoid the issues of tumbling, barrel rifling and spin.
Some of the advantageous features of the air gun disclosed herein include:
- Semi-automatic repeater, firing one projectile for each pull of the
trigger, and
automatically reloading + resetting itself to be ready for the next pull of
the trigger.
- Replaceable magazine.
CA 02756606 2011-11-01
- Able to be operated by one hand. 21
- multi-functional use of the bolt, including acting as a high speed valve
for
introducing the HPA to the receiver from the dump chamber via the receiver
ports
uncovered by initial displacement of the bolt.
Since various modifications can be made in my invention as herein above
described, and many apparently widely different embodiments of same made
within
the spirit and scope of the claims without department from such spirit and
scope, it is
intended that all matter contained in the accompanying specification shall be
interpreted as illustrative only and not in a limiting sense.
