Projectile

A tubular projectile having a venturi throat configuration is disposed with rifling on the interior wall surfaces providing a highly aerodynamic projectile which can be used in smooth bore barrel artillery.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to projectiles and more particularly to 
rifled bullets for use in smooth bore gun barrels. 
2. Description of the Prior Art 
There has been an increased interest in recent years in the use of slugs 
especially for the hunting of large game animals. Conventional slugs known 
in the art tend to consist of a solid mass of lead with a relatively blunt 
nose and generally cylindrical body. These solid lead slugs were 
optionally equipped with helical ribbing disposed about the outer 
periphery of the slug. The incorporation of the helical ribbing (rifling) 
imparts a spin to the projectile while in flight and creates a generally 
more aerodynamic slug. However, many hunters have complained that even 
with the outer rifling these solid lead slugs were inaccurate, had a short 
effective range and lacked knockdown power. Furthermore, these rifled 
slugs could not be utilized in a traditional smooth bore barrel shotgun as 
they would cause undue wear and leading to the inner barrel surface and 
accuracy and gyration would both be significantly impaired. 
Attempts have been made to overcome these problems of the prior art by 
manufacturing projectiles from lighter weight materials or alternately 
providing a hollow center passage through the projectile such as to form a 
tubular shape. The tubular projectile has especially proven to possess 
certain advantages over previous projectile designs as the tubular passage 
significantly reduces ballistic drag and shock wave and increases impact 
force and target penetration. The tubular projectile can optionally be 
provided with the outer helical rifling to impart a gyration on the 
airborne projectile. Variations in the size and shape of the hollow center 
passage have been demonstrated such as expanding the size of the inlet 
area aperture and providing thicker passage walls with varying success 
rates. It has been therefore concluded that minor changes of contour can 
make a decisive difference in the success or failure of the design in 
terms of its ballistic and aerodynamic characteristics. A particularly 
desirable design has proven to consist of a hollow passage wherein the 
inner surface gradually tapers inwardly converging toward a throat section 
immediately followed by a divergent aft section. The incorporation of the 
throat section has been shown to optimize many of the critical ballistic 
characteristics. However, when rifling is included on the exterior surface 
of this throated slug, its use in smooth bore shotguns is questionable. 
A longfelt need has therefore existed in the prior art for the development 
of an extremely accurate tubular slug for use in a smooth bore barrel 
shotgun which still intrinsically spins during flight producing gyroscopic 
stabilization. 
SUMMARY OF THE INVENTION 
The present invention employs a throated tubular projectile wherein helical 
rifling is provided on the inner surface walls such that it can be loaded 
in a smooth bore barrel shotgun without compromising ideal aerodynamic 
characteristics. Thus, the novel provision of helical rifling on the 
interior projectile walls induces rotation of the slug identical to the 
rotation effects of exterior rifling. The hollow design forces airflow to 
enter the center passage of the slug as the slug travels through the air; 
the forceful flow of air over the helical grooves inherently causes the 
slug to rotate producing superior aerodynamic effects. Stability is 
further enhanced with the incorporation of a venturi throat passage shape. 
The air inlet aperture is at a maximum diameter thereby permitting the 
greatest possible volume of air into the interior of the slug. The 
interior walls then converge rearwardly, approximately 3/4 the length of 
the projectile, to a point of minimum diameter, then immediately diverge 
outwardly at approximately the same pitch as convergence, climaxing at the 
exit aperture such that the exit aperture possesses a diameter which is 
substantially larger than the minimum point (venture throat point), but 
does not surpass the cross-sectional area of the air inlet aperture. The 
provision of the venturi type throat design reduces pressure as the air 
must compress to achieve the minimum cross-sectional area, thereby 
stabilizing the flight of the bullet and reducing drag, bases vacuum and 
shock wave or head pressure. The slug might optionally be provided with a 
plurality of small radial holes from the venturi throat to the outer 
surface of the slug. These radial holes minimize turbulence of the air 
passing through the throated passageway, and prevent chocking above mach 4 
thus further stabilizing the flight of the projectile. These holes may be 
at a trailing compound angle to the axis so that they help to impart spin 
to the slug, or they may be perpendicular to the axis. 
It is the combination a venturi throat, interior rifling and optional 
radial holes which define a superior tubular projectile for use in a 
smooth bore barrel shotgun. 
Accordingly it is an important object of the present invention to provide 
an improved projectile for use in a smooth bore barrel. 
A further object of the present invention is to provide the novel use of 
rifling on the interior walls of a projectile. 
Another object of the present invention is to provide a combination of 
several separate features to effectively maximize aerodynamic 
characteristics and reduce ballistic drag, and shock wave or head 
pressure. 
Further objects and advantages of this invention will be apparent from the 
following detailed description of a presently preferred embodiment which 
is illustrated schematically in the accompanying drawings.

Before explaining the disclosed embodiment of the present invention in 
detail it is to be understood that the invention is not limited in its 
application to the details of the particular arrangement shown since the 
invention is capable of other embodiments. Also, the terminology used 
herein is for the purpose of description and not of limitation. 
DETAILED DESCRIPTION OF THE DRAWINGS 
Referring now in detail to FIG. 1, a projectile is illustrated generally at 
1. As shown, projectile 1 is disposed within a conventional shell casing 2 
and is oriented flush against a nylon pusher 4. The pusher 4, best shown 
in FIG. 6, preferably has either a triangular, pentagonal, hexagonal or a 
conical diameter (frustum of cone) terminal end 21 which contacts the 
projectile 1 when oriented in a typical arrangement. The pusher 4 further 
contains a flange member 22 which acts as a support that prevents 
deformation. The shotgun acts as a solid barrier thereby allowing the 
projectile 1 to eject from the casing 2 and out the terminal end of the 
gun barrel (not shown). For 383 PCC or 357 MAG in a rifled barrel a gas 
check 15 may be incorporated into the pusher or may be part of the wad or 
a separate item to establish proper wad column height for crimping, 
allowing for clean firing and increased projectile velocity. The powder 
chamber 16 is behind the gas check. 
FIG. 2 shows the projectile 1 in greater detail. the inventive structure is 
an elongate tubular body member with a center hollow passage 13 extending 
therethrough and is symmetrical about a center longitudinal axis 18. The 
outer surface 19 of the body member is essentially smooth and may 
optionally contain a plurality of radial holes 20 which penetrate 
completely through the body member, effectively extending from the outer 
surface 19 to the inner surface walls 9, 10. The radial holes 20 minimize 
turbulence of the air flowing through the hollow passage 13 and prevent 
chocking when the projectile 1 is in flight. The holes 20 may be oriented 
either perpendicular to the center axis 18, as shown in FIGS. 2 and 3, or 
they may be at a compound angle to the center axis, as shown at 20' in 
FIGS. 8 and 9, to complement spin. The projectile 1 is comprised of two 
sections 6,8 intersected by a single plane throat 7 of minimum diameter. 
The forward inner surface walls 9, initiating at the air inlet aperture 
12, converge rearwardly until reaching the throat 7, thereby defining the 
forward compression section 6. After attaining the point of minimum 
diameter 7, the rear inner surface walls 10 begin to diverge outwardly at 
approximately the same pitch as convergence until reaching the exit 
aperture 11. The rear divergence section 8 is thereby defined with the 
throat 7 and the exit aperture 11 as its confining limits. 
This projectile design drastically reduces drag, shock wave and turbulence 
and allows for maximized velocity levels. After launch from the gun 
muzzle, air enters the projectile 1 through the air inlet aperture 12. The 
air immediately becomes compressed due to the converging inner wall 
surfaces 9; upon reaching the sharp edged throat 7, the air will be 
instantaneously forced to diffuse outwardly while traveling through the 
rear divergence section 8 such that an essentially steady state flow 
condition is achieved as the air evacuates the projectile 1 through the 
exit aperture 11. It will blow away the pusher and wads. Any turbulence 
generated from successive compression and diffusion of the air will be 
significantly circumvented by the incorporation of the radial holes 20 on 
the body member's outer surface 19. The end result includes an extremely 
effective projectile 1 whereby the venturi type throat design stabilizes 
the direction and velocity of the projectile 1 as it is in flight, thereby 
increasing the external ballistics by significantly depreciating drag. 
The inner wall surfaces 9,10 are disposed with 12-14 flutes of high thin 
helical ribbing known as rifling 5. The rifling 5 may be oriented on both 
inner wall surfaces 9,10 or in a second embodiment, only the forward inner 
surface walls 9 are provided with rifling 5. As air enters the center 
passage 13, the rifling 5 acts to force the air flow in a circular 
direction causing a gyration or spinning of the projectile 1 as it is in 
flight. The rotating action of the projectile 1 creates a more stable slug 
and improves its inherent accuracy. 
FIGS. 7, 8 and 9 show a second embodiment of the invention which is 
identical to the embodiment of FIGS. 2-6 except that it has transverse 
holes 20' extending from the periphery 19' of the hollow body into the 
throat 7' of its venturi passageway at a compound angle to the axis of 
this passageway instead of perpendicular to it. 
The projectile and pusher of the instant invention may be packaged in any 
conventional shotgun shell or other encasing known in the art. It is 
anticipated that the projectile is particularly well adapted for use in a 
smooth bore barrel gun and especially a shotgun or smooth bore artillery. 
The projectile may be made of metal such as lead or high density 
thermoplastic or polymers. The latter have superior wear resistance, 
dimentional stability and low cost per cubic inch. When fired into hard 
wax, a lead projectile will double its diameter. When fired into aluminum 
or steel it will punch out a plug and then form a ball and go through.