Plastic cartridge case

An all-plastic cartridge case is disclosed. The case is all-plastic and has a hard-plastic rim and a soft-plastic basewad. The basewad is of a plastic similar to that of the shotshell tube while the rim is of a plastic which is chemically dissimilar to the tube. The basewad and rim are mechanically interlocked. Also disclosed is a two-step method for molding such a shell with a dual plastic head. Either the rim or the basewad is molded first and the other of the two is molded through the first.

BACKGROUND AND SUMMARY OF INVENTION 
This invention relates to non-metallic shotshells and more particularly to 
all plastic shotshells. 
Conventional all-plastic shotshells all suffer from a common problem. They 
do not feed reliably from semi-automatic shotguns but instead suffer rim 
shear problems. A solution to this problem is needed. A one-piece, hard 
plastic head may be molded using nylon, polycarbonate and similar resins 
on one end of an extruded polyethylene tubing to form an all-plastic 
cartridge case and the molded hard head would, prior to firing, adhere to 
the tubing and withstand (for example, in 12 gauge shells) 100 or more 
pounds of head pulling forces. However, when such hard-headed shotshells 
are fully loaded into shotshell rounds and are test fired in pressure 
barrels or guns, the heads become loose from the tubing and often fall 
off. It appears to applicants that, upon firing, the adhesion of the hard 
nylon and such other plastic heads to polyethylene tubing is insufficient 
to withstand firing forces as the two plastic materials are incompatible, 
being immiscible and so do not form a strong enough initial chemical bond. 
Even the conventional pretreatment of the polyethylene tubing with chromic 
acid, chlorine or flame does not improve the adhesion of the hard head 
plastic to the polyethylene tubing upon firing. Thus, plastic shotshell 
manufacturers have uniformly only used head materials which are chemically 
similar to the plastic tube, thus sacrificing rim quality in order to have 
an adherent head to prevent gas leakage. Also, it has traditionally been 
felt by ammunition makers that hard plastic heads would be too brittle at 
low temperatures to withstand high firing pressures and would result in 
cracked heads, a critical defect. 
The present invention solves the above problems by providing a cartridge 
case without metallic reinforcement portions, comprising an exterior 
tubular body of plastic having a base end; an internal adherent plastic 
basewad molded to the inside surface of the base end of said body and 
having an axial opening adapted to receive a primer and having one or more 
interlock channels therein; an exterior hard, tough plastic rim molded 
into mechanically interlocked attachment to said interlock channels of 
said basewad, said rim being of a material chemically dissimilar from and 
not chemically adherent to either of said tubular body and basewad.

Referring to FIGS. 1-3, an extruded polyethylene tube 10 (preferably a 
biaxially oriented tube of the Reiferhauser type) such as that shown in 
FIG. 1, of suitable length, diameter, and wall thickness is inserted into 
a mold. A perforated, high density polyethylene ("HDPE") basewad core 12 
is then injection molded to the interior of tube 10 to produce an unrimmed 
intermediate shotshell tube 11 as seen in FIG. 2. Next, a hard plastic rim 
body 13 is injection molded into and behind basewad core 12 to produce a 
hard-rimmed, all-plastic shotshell 14. As a preferred alternative, a hard 
plastic rim body 15 can be injection molded onto the base of tube 10 as 
seen in FIGS. 5-6 and then a HDPE basewad core 16 can be injection molded 
behind, through, and in front of rim 15 to mechanically lock rim 15 into 
place at the base of tube 10 to produce a hard-rimmed, all-plastic 
shotshell 17. 
Referring to FIGS. 3 and 5, shotshells 14 and 17 comprise a sandwich 
construction with a HDPE (with or without fillers) core 12 or 16 and a 
hard nylon or polycarbonate rim 13 or 15 on the top and bottom axially of 
the HDPE core. This is achieved by a two-step molding. In one step, a thin 
head of the said polyethylene is molded about 0.1" to 0.5" deep inside one 
end of the tube 10 with excellent chemical bonding to the walls of tube 10 
to form the central layer of the proposed sandwich. Additionally, this 
HDPE head core is provided in the molding operation with a hole in the 
center for later seating of a primer (not shown). In the other step, a 
second hard and tough plastic, such as nylon, polycarbonate, 
polyethylene-terephthalate, butylene-terephthalate, or 
styrene-acrylonitrile copolymer and other similar hard and tough resins, 
is molded onto the bottom of tube 10. The molten second resin flows 
through the portion deposited in the first step. If the core 12 is molded 
first, the rim is injected below, through, and above core 12 to form a 
hard surface on both sides of the polyethylene core 12. Alternatively, the 
hard rim 15 can be first injection molded onto the bottom end 18 of tube 
with a radial internal locking projection 20 being molded onto rim 15. A 
subsequently molded basewad core 16 then mechanically locks around 
projection 20, thus minimizing and restraining axial movement and provides 
added support to any primer later seated inside the resulting shotshell 
17. The core 16 can be made of a plastic which is chemically similar to 
tube 10 so that core chemically bonds with the tube to an upper monobloc 
portion of shotshell 17. The hard, plastic rim 13 or 15 is thus 
mechanically locked to the bottom of a core 12 or 16 which is in turn 
strongly bonded to tube 10. 
It is preferred that the primer pocket 22 be lined with polyethylene or 
other relatively soft plastic so that gas leaks through the primer port 
and dropped primers are avoided and no cracks or splits are produced when 
the primer ignites. Also, there is no hard plastic at the top of basewad 
16 so that cracking of the basewad top is reduced or eliminated. 
Unexpectedly, we have found this construction provides high strength, 
integrity, and adhesion of the dual plastic head to the polyethylene 
tubing. Nylons, in general, have served as the best second hard plastic. 
Polycarbonate (or its alloys with polyethylene or ABS) is the next best 
resin. Shotshell cartridge cases and centerfire cartridge cases such as 
Caliber .38 Special and Caliber .45 Auto have been made as per this 
invention and tested. 
"Hard and tough plastic" as used herein means a plastic material which can 
withstand the harsh magazine feeding forces of semi-automatic shotguns 
such as the Remington Model 1100 or Winchester Model 1400. In addition to 
the magnitude of the forces of such semi-automatic guns, there is the 
additional consideration that the feeding mechanisms were designed years 
ago on the premise that metal headed shells would be used. Applicants have 
found that these mechanisms, having been designed for metal rims, tend to 
slice through or ride over the rim if it is too soft or break or chip the 
rim if it is too brittle, thus jamming the gun. One conventional measure 
of hardness of plastics is the Shore D Hardness test according to ASTM 
Standard No. D2240. It has been found that a Shore D hardness of greater 
than about 70 at 70.degree. F. (21.degree. C.) is needed for consistent 
resistance to rim shearing or rim ride over (rim bending). A second 
hardness measure is the Rockwell hardness number according to ASTM 
Standard Test Method No. D-785. It has been found that a Rockwell hardness 
of greater than about R80 at 70.degree. F. (21.degree. C.) is sufficient 
to provide consistent resistance to rim shearing or rim bending. 
Hardness alone is insufficient, as the plastic rim must not be so brittle 
that it cracks or shatters at cold temperatures, since a cracked head is 
generally considered to be a critical defect due to the probability of gas 
leaks through a cracked head. It has been found that the plastic rim will 
consistently resist cracking if it has an Izod Impact Strength of greater 
than 5 ft-lbs per inch of notch (270 Joules/meter of notch) at 0.degree. 
F. (-18.degree. C.) as based on ASTM Standard Test Method D256. 
Another criteria of the plastic rim is that the plastic should provide the 
desired characteristics at minimum cost so that the advantages of the 
invention can be commercially realized. It would make little commercial 
sense to develop an all-plastic shotshell if it is more costly than a 
metal headed shotshell unless, of course, there were offsetting added 
benefits in performance. Nevertheless, this invention contemplates that 
new, better, cheaper plastics may arise. Some currently technically 
suitable materials such as the polyetherimide sold by General Electric 
under the trademark ULTEM, high-strength, reaction-injection-molded 
polyurethanes, polyphenylene sulfide and others, which are presently too 
expensive, could become economically feasible in the future. 
The primary advantage of the present invention is its ability to function 
reliably in even the most unfavorable conditions in semi-automatic 
shotguns without rim shear, gas leakage, dropped primers, or other 
critical defects. Another significant advantage of the invention is its 
ability to be reliably reloaded and reused. The shotshell of the invention 
recognizes the need for shotshells to have materials of high shear 
strength at the rim and of high longitudinal and circumferential tensile 
strength in the tube and basewad while keeping the dissimilar meterials 
locked together during both initial firing and refiring after reload. 
These dissimilar needs had, until the present invention, lead the major 
shotshell producers away from all-plastic shells. 
EXAMPLE 1 
A Reifenhauser-type extruded polyethylene tube 10 of 0.780" outside 
diameter and 0.730" inside diameter was cut to 2.75" length (FIG. 1). This 
tube 10 was placed in a mold cavity, assembled in an injection molding 
machine, and high density polyethylene was injected into the inside of the 
tube 10 to form the core with several holes as shown in FIG. 2. This 
tubing with polyethylene core was moved to another mold cavity in a second 
injection molding machine and Nylon 66 was injected to form the rim 13 at 
the bottom and also for the nylon to flow through the holes in the 
polyethylene core and form a thin layer on the other side of the core 12 
to lock the nylon section, and thus forming an all-plastic, hard-rimmed 
duobloc shotshell cartridge case 14. 
This case 14 is assembled with a shotshell primer (for example, Olin's 
209-955 primer), loaded with a conventional powder charge of 23.5 grains 
of Olin's WC473 nitrocellulose propellant powder, a conventional plastic 
wad with 11/8 ounces of lead shot number 71/2 (diameter 0.095") and the 
mouth of the shotshell case is closed by conventional crimping. In 
accordance with conventional testing procedures, the loaded rounds are 
"conditioned" and fired in a pressure barrel at 0.degree. F., 70.degree. 
F., and +125.degree. F. for pressure and velocity with the following 
results. 
TABLE I 
______________________________________ 
PRESSURE (PSI) AND VELOCITY (FPS) 
10 ROUNDS FIRED AT EACH TEMPERATURE 
Temperature 
Average Pressure (psi) 
Average Velocity (fps) 
______________________________________ 
0 10,400 1196 
70.degree. F. 
9,900 1211 
125.degree. F. 
10,400 1231 
______________________________________ 
After firing, the cartridge cases are examined and found to be intact. The 
plastic head retained its integrity. 
When shotshell cartridges, with only Nylon 66 head (no polyethylene core) 
molded on Reifenhauser extruded tubing, are loaded as above and fired in 
the pressure barrel, the following results are obtained. 
______________________________________ 
Temperature 
Average Pressure (psi) 
Average Velocity (fps) 
______________________________________ 
0 8,600 1103 
70.degree. F. 
9,500 1175 
125.degree. F. 
9,800 1186 
______________________________________ 
After firing the cartridge cases are examined and we find that the nylon 
heads are loose from the tube and come off easily. 
The shotshell cartridges 14 and 17 of this invention were fired for 
function and casualty in Winchester Super-X Model 1, Remington Model 1100 
and Winchester Model 1400 at 0.degree. F., 70.degree. F. and 125.degree. 
F. with good results. The shotshell cartridges were reloaded and fired 
five times in Remington Model 870 gun without any defects observed. The 
reloadability of the cartridges ten times was 96 to 97 percent. Under 
these reloading conditions, the dual hard plastic head stays on the tube 
and retains its integrity. 
EXAMPLE 2 
0.410 gauge Reifenhauser extruded polyethylene tube was cut to 1.15" length 
and a dual plastic head of polyethylene and nylon was molded on one end of 
the tube. The cartridge case was loaded with Olin's 108 primer and fired 
in a pressure barrel to test the strength of the head. The head stayed 
intact, retaining its integrity. 
EXAMPLE 3 
Another tube 10 of 0.780" outside diameter and 0.730" inside diameter is 
cut to 2.75" length as in FIG. 5. This tube 10 is placed in a mold cavity, 
assembled in an injection molding machine and a Nylon 66 base rim 15 is 
molded onto the bottom 18 of tube 10 and weakly adheres there to and forms 
the rim shape shown in FIG. 5 with internal locking projections 20. This 
tube with base rim is moved to another cavity in another injection molding 
machine and an HDPE basewad 16 is molded below through and above the rim 
15 and into strong chemical bonding with the inner wall of tube 10 and 
strongly mechanically locking around projections 20, thus forming an 
all-plastic, hard-rimmed duobloc shotshell. This case is loaded and fired 
as in Example 1 above, no internal or external defects are noticed. The 
rim is not sheared in the Winchester 1400 semi-automatic sporting 
shotguns, which from prior testing shear the rims of all commercially 
available all-plastic shotshells.