Base insert for polymer ammunition cartridges
An insert for a high strength polymer-based cartridge casing can include an outside, an inside formed within the insert, and a back end disposed at a rear of the cartridge casing. The back end includes a rim and groove disposed around the outside of the insert and a primer pocket disposed inside the back end. Also included is a front end, opposite the back end, having an overmolded area disposed around the outside of the insert above the primer pocket and a basin, having a depth, formed inside the overmolded area. A flash hole can be included inside the insert and communicating between the primer pocket and the basin. The flash hole has a perimeter and a ring disposed around the perimeter of the flash hole, including a height starting at a bottom of the basin, disposed toward the front end, and less than the depth of the basin.
1. A high strength polymer-based cartridge casing comprising:
a cartridge body, molded from a polymer, comprising:
a first end having a mouth; and
a second end opposite the first end;
an outer sheath disposed proximate the second end;
a lower bowl disposed proximate the outer sheath and having a hole therethrough;
an insert, formed from at least one of a metal and metal alloy, comprising a front end and a back end, and further comprising:
a rim disposed at the back end;
a primer pocket disposed at and open along a portion of the back end and continuing partially toward the front end;
a flash hole disposed forward of the primer pocket, in fluid communication with the primer pocket, and continuing partially toward the front end; and
an overmolded area formed at the front end, opposite the rim, comprising:
a basin formed on an inside of the overmolded area and disposed above the primer pocket; and
a ring formed, at a bottom of the basin, on an inside of the overmolded area, and surrounding the flash hole, comprising a ring wall;
wherein the ring prevents polymer from the lower bowl from flowing into the flash hole by stopping the polymer at the ring wall;
wherein the second end of the cartridge body engages with the front end of the insert;
wherein the outer sheath is disposed to an outside of the overmolded area;
wherein the lower bowl is disposed inside of the overmolded area and in contact with the basin; and
wherein the hole in the lower bowl is disposed around the ring wall.
2. The high strength polymer-based cartridge casing of claim 1 , wherein during a powder ignition in a firearm, the lower bowl presses against the basin and the outer sheath contacts the firearm to create a compression effect against the overmolded area.
3. The high strength polymer-based cartridge casing of claim 1 , wherein the insert further comprises:
a ridge formed on the overmolded area; and
a key formed on the ridge;
wherein both the ridge and the key engage the outer sheath, and
wherein the key comprises at least one of a flat portion, a raised portion, or dimples.
4. A method of making a high strength polymer-based cartridge casing comprising the steps of:
forming an insert from at least one of a metal and metal alloy, comprising a front end and a back end, and further forming:
a rim disposed at the back end;
a primer pocket disposed at and open along a portion of the back end and continuing partially toward the front end;
a flash hole disposed forward of the primer pocket, in fluid communication with the primer pocket, and continuing partially toward the front end; and
an overmolded area formed at the front end, opposite the rim, comprising;
a basin formed on an inside of the overmolded area and disposed above the primer pocket; and
a ring formed, at a bottom of the basin, on an inside of the overmolded area, and surrounding the flash hole, comprising a ring wall;
molding a cartridge body using a polymer comprising the steps of:
molding the polymer to form an outer sheath disposed proximate the second end and to an outside of the overmolded area;
molding a lower bowl disposed proximate the outer sheath, inside of the overmolded area, in contact with the basin, and having a hole therethrough; and
stopping the polymer at the ring wall.
5. The method of making a high strength polymer-based cartridge casing of claim 4 , wherein forming the insert further comprises the steps of:
forming a ridge on the overmolded area; and
forming a key on the ridge with at least one of a flat portion, a raised portion, or dimples;
wherein both the ridge and the key engage the outer sheath.