Reduced drag projectiles
Embodiments of the invention include an elongate rifle bullet with a plurality of circumferential grooves having overmolded polymer therein defining embedded polymer rings. Embodiments of the invention include cartridges with propellant and such bullets. In one or more embodiments, the bullet has a body portion and a converging nose portion. The polymer rings have an outer surface that is flush with, that is, conforming to the outer surface of the body. The polymer may have be selected to have a favorable coefficient of friction with respect to the barrel. A feature and advantage of embodiments is that the metal to metal contact between the bullet and the barrel is reduced while not diminishing the ballistic coefficient of the bullet.
1. A method of manufacturing a bullet of .50 caliber or less, the method comprising:
obtaining a bullet body defining a plurality of circumferential grooves, each circumferential groove having a pair of adjacent wall portions, the bullet body comprising a body wall extending between an interior wall surface and an exterior wall surface, the interior wall surface defining an interior cavity, the interior cavity fluidly communicating with an opening defined by a forward facing edge of the bullet body, the interior cavity extending rearwardly from the opening to a cavity end point within the bullet body, a core member disposed inside the cavity, the core member comprising a forward facing surface, the core member extending rearwardly from the forward facing surface to the cavity end point within the body, the forward facing surface of the core member and the interior wall surface defining a forward portion of the interior cavity, the forward portion of the interior cavity having a cavity radius, the cavity radius decreasing as the forward portion of the interior cavity extends forward from the forward facing surface of the core member to the opening;
inserting the bullet body into a mold with one or more groove sprues, the mold having a mold wall surface that is flush at the location of each of the plurality of grooves and the exterior wall surface at the respective adjacent wall portions to each of the plurality of grooves;
injecting molten polymer into the plurality of grooves through the one or more groove sprues;
allowing the polymer to cool forming a plurality of polymer bands, each polymer band being disposed in one of the plurality of circumferential grooves; and
removing the bullet body from the mold.
2. The method of claim 1 further comprising:
injecting molten polymer into the forward portion of the interior cavity through at least one tip sprue; and
allowing the polymer to cool forming a polymer tip, the polymer tip comprising a forward portion extending forward of the opening and a rearward portion extending rearward of the opening, the rearward portion having a shape corresponding to the forward portion of the interior cavity to retain the polymer tip in place.
3. The method of claim 2 wherein molten polymer is injected into the plurality of grooves through the one or more groove sprues into the plurality of grooves while molten polymer is being injected into the forward portion of the interior cavity through the at least one tip sprue.
4. The method of claim 1 further comprising providing a mold defining a tip cavity fluidly communicating with at least one tip sprue.
5. The method of claim 2 , further comprising selecting a mold wherein each of the one or more groove sprues is in fluid communication with the at least one tip sprue.
6. A method of manufacturing a bullet of .50 caliber or less, the method comprising:
providing a bullet body defining a plurality of circumferential grooves, each circumferential groove being defined by a groove root surface of the bullet body and a pair of opposing groove side surfaces, each opposing groove side surface extending between the groove root surface and a barrel engaging surface of the bullet body, wherein the bullet body is continuous and of a single material when viewed as a cross-section with a section plane passing through the groove root surface;
inserting the bullet body into a mold with one or more groove sprues, the mold having a mold wall surface that is flush at the location of each of the plurality of grooves and an exterior bullet body wall surface at the respective adjacent wall portions of each of the plurality of grooves;
injecting molten polymer into the plurality of grooves through the one or more groove sprues;
allowing the polymer to cool forming a plurality of polymer bands, each polymer band being disposed in one of the plurality of circumferential grooves and having an exterior surface flush with the exterior bullet wall surface;
removing the bullet body from the mold; and
inserting the bullet body into a casing with propellant in the casing.
7. The method of claim 6 further comprising providing the bullet body as monolithic and of a single material.
8. The method of claim 7 further comprising selecting the single material of the bullet body to be copper or a copper alloy.
9. The method of claim 6 further comprising integrally forming the bullet body from a unitary piece of material.
10. The method of claim 6 further comprising selecting a polymer to have a minimal coefficient of friction with respect to the steel barrel.
11. The method of claim 6 further comprising heating the bullet body prior to the injection of the polymer whereby the polymer adhesion to the bullet body is enhanced.
12. The method of claim 6 further comprising undercutting each of the plurality of grooves.
13. A method of manufacturing a bullet of .50 caliber or less, the method comprising:
providing a bullet body defining a plurality of circumferential grooves, each circumferential groove being defined by a groove root surface of the bullet body and a pair of opposing groove side surfaces, each opposing groove side surface extending between the groove root surface and a barrel engaging surface of the bullet body, wherein the bullet body is continuous when viewed as a cross-section with a section plane passing through the groove root surface and the bullet body has no separate core at the cross-section;
inserting the bullet body into a mold with one or more groove sprues, the mold having a mold wall surface that is flush at the location of each of the plurality of grooves and an exterior bullet body wall surface at the respective adjacent wall portions of each of the plurality of grooves;
injecting molten polymer into the plurality of grooves through the one or more groove sprues;
allowing the polymer to cool forming a plurality of polymer bands, each polymer band being disposed in one of the plurality of circumferential grooves and having an exterior surface flush with the exterior bullet wall surface;
removing the bullet body from the mold; and
inserting the bullet body into a casing with propellant in the casing.
14. The method of claim 13 further comprising providing the bullet body as monolithic and of a single material.
15. The method of claim 14 further comprising selecting the single material of the bullet body to be copper or a copper alloy.
16. The method of claim 13 further comprising integrally forming the bullet body from a unitary piece of material.
17. The method of claim 13 further comprising selecting a polymer to have a minimal coefficient of friction with respect to the steel barrel.
18. The method of claim 13 further comprising heating the bullet body prior to the injection of the polymer whereby the polymer adhesion to the bullet body is enhanced.
19. The method of claim 13 further comprising undercutting each of the plurality of grooves.