Note: Descriptions are shown in the official language in which they were submitted.
2l8990q
Title: LIVE FIRE EXCLU8ION FOR AUTONATIC FIREARN8
Field of the Invention
This invention relates to the field of firearms and
provisions for modifying semi-automatic and fully automatic
firearms for training purposes. In particular, it relates to
a safety feature for firearms that have been modified to fire
blanks or sub-calibre, low energy ammunition.
Background to the Invention
In military and police firearms applications almost
all the ammunition consumed is used in training. For some
training purposes, however, normal ammunition is not adequate.
An alternate type of known training ammunition represented by
United States Patent No. 5,359,937 fires a low mass projectile
relying on a special cartridge design to provide cycling of
recoil-operated automatic weapons.
When such training rounds are being employed, it is
important to ensure that no weapon is loaded with standard,
live ammunition. An advantage of the lighter-weight training
ammunition is that it has a shorter range and lower
penetration capacity. This permits use of smaller, less
secure firing ranges as training facilities. If standard
ammunition were accidentally employed in these facilities,
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unexpected dangers would arise from the increased striking
power and range of standard ammunition.
To provide increased security when training rounds
are being employed, it has become conventional to provide
firearms with substitute barrels which are bored to fire a
smaller calibre round than standard ammunition. If an attempt
is made to chamber a standard round in a training-adapted
firearm, then the barrel will not normally admit entry of the
standard projectile. This ensures that such modified weapons
cannot fire standard, live ammunition. Other examples of
systems for converting standard firearms for operation with
sub-calibre ammunition vis U.S. Patent Nos. 4,515,004 and
4,531,446.
As one of the objectives in providing training
ammunition is to simulate use of a normal weapon as nearly as
possible, it has been customary to modify standard weapons
only to a minimum extent. In particular, subcalibre training
rounds are employed which have standard-sized casings. This
allows all parts of the weapon concerned with the loading and
cycling functions to operate in a nearly normal fashion. To
accommodate reduced recoil as provided by the cartridges of
U.S. Patent No. 5,359,937, springs and other secondary
components may also be modified.
It has been found that standard ammunition may be
capable of being loaded into a barrel-modified weapon if the
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projectile is pressed back into the casing. In certain cases,
reduced propellent is provided in training cartridges
providing room in the casing for the projectile to be pressed
therein, shortening the cartridge. By so shortening the
cartridge, it is possible that a live round has been chambered
within a weapon with a modified barrel. Upon firing such a
round, the projectile or a part thereof, can be extruded by
the high chamber pressure to travel down the barrel and out
the muzzle at a sufficiently high velocity to cause serious
bodily harm should it inadvertently strike a human target.
Conversely, should the projectile jam in the barrel and block
it the pressure build-up will blow open the breech at
considerable risk to the operator.
This invention addresses such a situation. In
particular, this invention provides a safety feature which
will prevent any portion of the projectile from exiting the
muzzle when a live cartridge is chambered and fired in a
firearm having a barrel bore of reduced diameter. This is
effected by allowing the cartridge casing to burst in a
controlled manner without danger to the operator.
In certain prior art firearms, the chambers of such
firearms have been provided with pressure-relief orifices
located rearward of the cartridge to serve as an escape path
for gases that may blow-back (e.g. from a burst primer cap).
Such orifices have been in the nature of a small hole that
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penetrated through the chamber wall of the firearm rearward of
the cartridge casing. By allowing for a secondary path for
gases to escape upon firing, the bolt and slide mechanism
barrel were protected against extreme over-pressures arising
from the use of a defective cartridge.
Such a relieve orifice was also effectively present
in early black-powder firearms that were fired through a
touch-hole.
In the prior art, however, no example is known of
provision for a casing to burst in the chamber and release
pressure through a pressure-relief orifice in the chamber
wall.
The invention in its general form will first be
described, and then its implementation in terms of specific
embodiments will be detailed with reference to the drawings
following hereafter. These embodiments are intended to
demonstrate the principle of the invention, and the manner of
its implementation. The invention in its broadest and more
specific forms will then be further described, and defined, in
each of the individual claims which conclude this
Specification.
Summary of the Invention
According to one aspect of the invention a firearm
is provided with a chamber for receiving a cartridge having a
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casing with a casing sidewall. The chamber is provided with
a pressure-relief orifice that extends through the chamber
wall to terminate adjacent to the casing sidewall. The
orifice is of sufficient diameter to allow the casing to burst
on firing and vent its gases through the pressure-relief
orifice, in the event that an excessive pressure condition
builds-up within the casing.
In particular, the invention is suited to weapons
having a barrel with a reduced bore diameter and a chamber
that will accommodate a standard sized round with a standard
diameter casing and projectile.
As a further feature of the invention, the pressure-
relief orifice may preferably be in the shape of one or more
elongated slots, for example of an elongated, oval shape, that
are oriented in parallel with the axis of the cartridge. More
preferably, such a slotted orifice may be located towards the
rearward end of the chamber wall. Further, it may extend so
as to run-out rearwardly so as to form a "u" shaped opening in
the chamber wall.
While the invention is of value with weapons
converted to fire sub-calibre ammunition, it may also be
utilized in weapons converted to fire blanks. An example of
such a system is depicted in U.S. Patent No. 5,433,134 wherein
the conversion barrel is substantially restricted by a plug
with a choking orifice.
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The foregoing summarizes the principal features of
the invention and some of its optional aspects. The invention
may be further understood by the description of the preferred
embodiments, in conjunction with the drawings, which now
follow.
Summary of the Figures
Figure 1 is a side view of a conventional automatic
pistol indicating the barrel and chamber portions.
Figure 2 is a sectioned side view of a prior art
conversion pistol barrel of reduced bore diameter.
Figure 3 is a view as in Figure 2 with the presence
of an elongated pressure relief slot formed according to the
invention, in the chamber wall of a pistol barrel wherein the
slot runs-out at the rearward end of the chamber wall.
Figure 4 is a top view of an automatic rifle or
machine gun barrel modified by the presence of an oval,
elongated pressure-relief orifice formed according to the
invention in the top mid-portion of the chamber wall.
Figures 5a and 5b are side views of cartridge
casings after they have been fired in barrels with modified
chambers in accordance with the invention corresponding to
Figure 3 (pistol casing) and Figure 4 (rifle or machine gun
casing) respectively.
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DescriPtion of the Preferred Embodiment
In Figure 1 an automatic pistol 1 is provided with
a barrel 2 having a chamber 3 and a slide 4 with an ejection
slot 5.
5In Figure 2 a conversion pistol barrel of prior art
design is shown wherein the barrel 2 has a bore 6 of reduced
diameter providing a conical forcing cone end 7 to the chamber
3. A cartridge 8 with a sub-calibre projectile 9 and full-
sized casing 10 is shown chambered in the barrel.
10In Figure 3 a pistol barrel modified according to
the invention has a pressure relief orifice 11 in the form of
a longitudinal extending opening that runs-out at the rearward
end of the chamber 3 to provide a "u" shaped slot in the
chamber wall that penetrates through to terminate adjacent to
15the casing 10 of the cartridge 12. The cartridge 12 is a live
round with a full sized projectile 13 shown compressed back
into the casing 10 from its normal position. This represents
a hypothetical situation where the live round 12 has been
forced into the chamber 3 notwithstanding the reduced diameter
of the barrel bore 6q~
Figure 4 is a top view of the barrel of an automatic
rifle or machine gun. The wall of the chamber 3 is provided
with a pressure-relief orifice lla in the form of a central,
elongated oval.
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The casing 10 of a cartridge inserted in the barrel
of Figure 4 (not shown) would partially burst along the
portion of the casing wall that is adjacent to the pressure-
relief orifice lla. The casing wall 14 would thereby be
sheared or torn to provide an opening of extended length to
form in the casing wall 14, facilitating the release of
pressurized gas from the cartridge 12.
In most cases, the slide 4 in a pistol or the bolt
17 in a rifle must be circled manually in order to remove the
spent cartridge 9,10 through the ejector slot 5.
Figures 5a and 5b show casings 10 after being
removed from a modified pistol or rifle/machine gun
respectively with the burst openings 14 apparent. The use of
a pressure-relief orifice lla of elongated shape, oriented
parallel to the cartridge axis, provides a preferred formation
of the burst openings 14. For example, the positioning of the
pressure-relief orifice 11 at the rearward end of the pistol
chamber 3, preferably running-out at the rearward edge of the
chamber 3, allows the burst opening 14 to commence anywhere
along the casing 10, but most likely near the cap end 16 of
the casing 10, extending down the side of the casing 10. By
extending the slot for almost the full length of the chamber
11, casings 10 can be caused to split along virtually their
full length.
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While use of a single pressure-relief orifice has
been shown, for security against excessive pressure build up,
two or more such orifices may be employed at spaced locations
around the circumference of the chamber 3.
Tests have been conducted in 9mm SIG P226, SIG 228,
SIG 229, Browning HP, Glock 17, Colt M16/K4, Beretta 92/96 and
Smith & Wesson 59 hand guns amongst others modified with
reduced diameter barrel bores to fire FXR rounds supplied by
SNC Industrial Technologies Inc. of Quebec, Canada. The
machined slot or pressure-relief orifice for the run-out slots
was 5/32 inch wide and 0.02-0.03 inches less than the chamber
length. Oval slots were approximately three times their width
in length. In no case did a normal-sized projectile proceed
down the reduced diameter barrel bore. In all examples, the
casings burst releasing the propellant
gases generated by such rounds.
Conclusion
The foregoing has constituted a description of
specific embodiments showing how the invention may be applied
and put into use. These embodiments are only exemplary. The
invention in its broadest, and more specific aspects, is
further described and defined in the claims which now follow.
These claims, and the language used therein, are to
be understood in terms of the variants of the invention which
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have been described. They are not to be restricted to such
variants, but are to be read as covering the full scope of
the invention as is implicit within the invention and the
disclosure that has been provided herein.
