Patent Publication Number: US-6216380-B1

Title: Breech plug primer cap adapter

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to muzzle loading firearms and, more particularly, to breech plugs which adapt the firearm to utilize percussion caps as the ignition means. 
     As is well known, percussion caps are preferred for ignition of the black powder charge in muzzle loading firearms, and various types of nipples using such caps have been developed. With the increasing use of inline firing systems because of better ignition characteristics, there has been a move to use primer or percussion caps in breech plugs providing such an inline firing system. Shotgun shell primer caps have been considered highly advantageous for use in such inline ignition systems. 
     There have been a number of breech plug constructions to adapt the muzzle loading firearm to use a primer cap which is detonated by a firing pin. The hot gases from the detonated primer cap travel in a passage through the plug to ignite the black powder at the barrel end of the breech plug. Exemplary of such structures are those illustrated in Carron U.S. Pat. No. 5,010,677 granted Apr. 30, 1991; Mahn et al U.S. Pat. No. 5,408,776 granted Apr. 25, 1995; and Osborne et al U.S. Pat. No. 5,487,232 granted Jan. 30, 1996. 
     The problems encountered in such breech plug adapters have included (i) holding the primer cap in the plug, (ii) expansion or deformation of the casing of the cap by the hot gases so as to make it difficult to remove from the plug, and (iii) contamination of the firing mechanism by the particles in the exhaust gases. Although it is necessary that the cap be securely seated in the plug, it is also necessary to be able to extract it readily from the plug. 
     It is an object of the present invention to provide a novel breech plug adapter for seating firing caps in an inline firing system for a muzzle loading firearm. 
     It is also an object to provide such a breech plug adapter which may be fabricated readily and relatively economically. 
     Another object is to provide such a breech plug adapter which seats the firing cap securely but avoids a tight friction fit which would make removal difficult upon expansion or deformation of the casing of the cap. 
     A further object is to provide such a breech plug adapter which diverts a substantial portion of the exhaust gases radially to the periphery of the plug to minimize distorting pressures on the casing of the cap and contamination of the bolt or other firing assembly. 
     SUMMARY OF THE INVENTION 
     It has now been found that the foregoing and related objects may be readily attained in a cap adapter breech plug for muzzle loading firearms which has a cylindrical plug with barrel and breech ends. A passage extending axially through the plug and a coaxial counterbore is provided about the passage at the breech end of the plug. An axial slot extends along a side of the counterbore and an exhaust passage extends generally radially from the passage adjacent the inner end of the counterbore to the outer surface of the plug for exhausting gases from the axially extending passage. A spring member is seated in the plug and has a portion extending through the axial slot and into the counterbore to bear resiliently against the casing of a cap seated in the counterbore to hold it in place. 
     Generally, the plug includes a well in the breech end adjacent to and communicating with the slot, and the spring has a body which is seated in the well and the aforementioned portion extends from one end of the body into the slot and into the counterbore. This portion of the spring is preferably of generally C-shaped configuration with its center section extending into the counterbore. 
     Desirably, the breech end of the plug also has a shallow channel extending radially from the well to the outer surface of the plug, and the body of the spring is of generally U-shaped configuration with an arm portion extending from its other end which is seated in the shallow channel. 
     Generally, the exhaust passage comprises a radially disposed exhaust channel extending to the outer periphery of the plug from a depth below the inner end of the counterbore. Desirably, it extends diametrically across the width of the plug and has a bottom wall which slopes downwardly from its outer end to the axis of the plug. 
     In a preferred embodiment, the bottom wall has a trough centrally thereof which extends to a depth below the inner end of the counterbore. In another embodiment, the exhaust passage comprises a radially extending bore extending from the coaxial passage below the counterbore. 
     The breech end of the plug also has a collar about the counterbore, and the breech plug has a body portion which is externally threaded for threaded engagement in the barrel of the firearm. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a side elevational view of a cap adapter breech plug embodying the present invention with a shotgun primer cap seated therein; 
     FIG. 2 is a cross sectional view of the breech plug of FIG.  1  and with the primer cap removed; 
     FIG. 3 is a plan view of the breech end of the plug; 
     FIG. 4 is a perspective view of the breech plug; 
     FIG. 5 is a side elevational view of the spring employed in the breech plug; 
     FIG. 6 is a perspective view of a breech plug utilizing another embodiment of gas exhaust passage; and 
     FIG. 7 is a cross sectional view of the breech plug of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1-4 illustrate a breech plug cap adapter embodying the present invention includes of a generally cylindrical breech plug generally designated by the numeral  10  with a breech end  12  and a barrel end  14 . A passage  16  extends coaxially therethrough and a counterbore  18  is provided in the breech end  12 . The exterior surface of most of the body  19  of the breech plug is threaded as indicated by the dotted lines  21  extending axially for engagement with internal threads in the barrel of the firearm (not shown). 
     A relatively shallow slot  20  extends radially from the counterbore  18  to a deeper well  22 , and a shallow channel  24  extends from the well  22  to the periphery of the plug  10 , all in radial alignment. Seated in the well  22  is the U-shaped body portion  28  of a spring generally designated by the numeral  26 . Extending from one leg of the body portion  28  is generally a C-shaped end portion  30  which seats in the slot  20  and partially extends into the counterbore  18 . Extending laterally from the other leg of the body portion  28  is an arm  32  which seats in the shallow channel  24 . 
     Extending diametrically across the breech end  12  of the plug  10  is a channel  34  which has a bottom wall  36  which slopes inwardly from the outer periphery to the axis of the plug  10 . The bottom wall has a groove  38  which extends to a point below the inner end of the counterbore  18  at the axis of the plug  10 . 
     Adjacent the barrel end  14  of the plug  10  the passage  16  has a reduced diameter portion  40  and the barrel end  14  has a conical recess  42  about the passage  16 . 
     The breech end  12  of the plug  10  has upstanding collar portions  46  about the counterbore  18 . As seen in FIG. 1, the rim  50  of the primer cap generally designated by the numeral  48  is spaced a short distance above the collar portions  46  to facilitate extraction of the spent cap. The casing  52  of the cap  48  fits snugly within the counterbore  18  and provides a chamber there within containing the primer powder charge (not shown). 
     In the embodiment of FIGS. 6 and 7, the exhaust passage comprises bores  44  extending radially from the coaxial passage  16  to the exterior of the plug. 
     When the firing pin on the bolt (not shown) of the firearm strikes the cap  48 , the powder charge therein is ignited and the flash extends through the passage  16  to the propellant powder charge (not shown) in the recess  42  to effect its ignition. The hot exhaust gases moving outwardly along the passage  16  are largely diverted into the channel  34  or through the bores  44  seen in FIG.  6  and thus do not expand the casing  52  or drive the cap into the firing pin. Moreover, diverting the exhaust gases away from the bolt assembly reduces its contamination. This also minimizes wear and corrosion of the firing mechanism. 
     In the present invention the counterbore can be dimensioned closely to the diameter of the casing of the firing cap seated therein but not to the point of frictional engagement. This allows some expansion of the casing by the exhaust gases without making extraction difficult. Generally, this will require a clearance of about 0.15 mm. 
     The C-shaped portion of the leaf spring resiliently bears on the casing side wall to retain it securely within the counterbore despite the clearance. 
     The breech plug is readily fabricated from bar stock and easily machined to provide the various slots, channels, passages, etc. The plug securely threads into the barrel of the firearm and is easily removed when so desired by engaging a wrench in the channel  34 . The spent cap can be removed readily from the breech plug by insertion of a tool under the rim of the cap and prying it outwardly. 
     Thus, it can be seen that the novel breech plug adapter of the present invention may be readily and economically fabricated to securely seat the primer cap while permitting its facile removal after firing. The hot gases from the powder ignition which travel back through the coaxial passage are largely oriented radially to the exterior of the plug rather than passing into and about the casing of the cap.