Patent Application
20100154270
This invention relates to muzzle loading firearms, and more particularly to removable breech closures.
Muzzle loading rifles have an essentially closed breech at the rear of the barrel, so that powder and bullets must be loaded at the muzzle or forward end of the barrel. A typical muzzle loading rifle has a barrel with a breech plug attached to occupy an enlarged internally threaded rear bore portion of the barrel at the breech end. In some rifles, the breech plug is permanently attached. In others, the breech plug is removable to facilitate pass-through cleaning of the bore.
A typical removable breech plug employs a finely threaded elongated body that screws into the rear of the barrel, with 10-15 turns to secure it in place. The barrel's rear end is internally threaded to receive the plug, which removes for cleaning (not for normal loading operations.) The cleaning process involves the passing of a rod with a brush at the end through the entire length of the barrel. The brush, wetted with a liquid cleaning agent, dissolves and dislodges fouling, and it is dragged out of an end of the barrel. The fouled brush may pass over the internal threads at the breech, allowing the threads to become fouled. This is a concern because the barrel threads are cut to a tight tolerance for a close fit with the plug threads, and minor fouling can make the plug difficult to reinstall or remove after reinstallation.
In addition, breech plugs are generally larger in diameter than the bore of the barrel. This means that the wall thickness surrounding the plug is thinner than it is just forward of the plug in the chamber. In at least some instances, this wall diameter at the plug may be a strength limitation, requiring a larger barrel diameter than otherwise would be required, increasing manufacturing cost and/or weight.
The barrel must be designed to provide an adequate safety margin to retain the breech plug even in overpressure circumstances in the chamber. The barrel must have adequate thickness to resist excessive expansion in such extreme circumstances, to ensure that the barrel's internal threads do not fail to retain the plug.
Further, the length of a breech plug must be greater than an adequate threshold to provide strength to retain the pressure in the chamber. This length extends the length of the barrel without extending the length from the breech face to the muzzle. The added barrel length increases the weight and cost without the performance advantages of a lengthened barrel.
The elongated breech plug is a solid steel mass with only a small central bore to provide a fire passage between a primer and the chamber. The plug itself has appreciable mass to fill the required length and diameter, with weight reducing measures being generally impractical, even though lightness is generally desired in many rifles.
The present invention overcomes the limitations of the prior art by providing a muzzle loading firearm having an elongated barrel defining an elongated bore, with a muzzle end and a breech end. A breech cap is removably connected the breech end of the barrel to enclose a chamber at the rear of the bore. A portion of the breech cap may be external to the barrel, which may be externally threaded. The breech cap may be entirely clear of the breech bore, and the bore may have a consistent profile from end to end. The barrel threads may be standard, multistart or interrupted. The breech cap may overlay the face of the rear end of the barrel.
The barrel assembly 12 includes a barrel 24 and a breech cap 26. The barrel has a muzzle end face 30 and a breach end face 32, each perpendicular to an axis 34 defined by the conventionally rifled bore 36. The bore extends for the entire length of the barrel, having a consistent profile from end to end. That is, it has a consistent diameter throughout the entire length defining a continuous cylinder, except for the variations inherent in conventional helical rifling. The grooves and lands of the rifling extend from end to end in the barrel, and each of the groove diameter and the land diameter remain constant throughout the length of the barrel.
A rear portion 40 of the length of the barrel nearest the breach end 32 is externally threaded to accommodate the removable breach 26. In the illustrated embodiment, the threaded portion extends between one and two times the barrel overall diameter. The threads are shown as buttress threads, to provide maximum strength in resisting rearward forces on the breech cap 26 due to expansion of propellant gases in the chamber to find at the rear end of the barrel's bore. Alternative thread arrangements are discussed below.
The barrel has a conventional exterior profile, in that it is cylindrical at the rear portion forward of the threaded portion. In various embodiments, external profile of the barrel may extend as a cylinder forward to the muzzle, or it may taper toward the muzzle. The largest diameter portion of the barrel is just forward of the threaded portion. The threaded portion has a maximum diameter less than or equal to the barrel maximum diameter. This allows the threads to be economically manufactured from a barrel blank of an appropriate limited diameter size. In the preferred embodiment, the barrel's maximum external diameter is 1.0 inch, the threaded portion has a length of 1.25 inch, with 10 buttress-type threads. The bore has a diameter of 0.500 inch, and the barrel has a length ranging between 24 and 30 inches.
The breech cap 26 is a generally cylindrical body having the shape of a cup, with a circular base 42 having a forwardly extending sleeve or rim 44. The base and rim define a forwardly-open cylindrical chamber 46 that is internally threaded with threads 50 that mate with the threaded portion 40 of the barrel. The base 42 defines a central axial cylindrical primer pocket 52 having a floor 54 that defines a central fire hole 56, which communicates with the cylindrical chamber 46. The forward surface 60 of the base provides a flat angular surface against which the rear face 32 of the barrel abuts. These surfaces are tightly abutted to provide a gas seal against escape of propellant gases from the chamber upon discharge. In alternative embodiments, the surface may be shaped differently, such as with a conical or dished contour, as long as a close fit and seal are formed.
In the preferred embodiment, the breech cap 26 has a length of 2.0 inches, and a diameter of 1.2 inch. The base 42 has a thickness of 0.50 inch, and the length of the fire hole is 0.125 inch. The diameter of the cap is slightly larger than the outside diameter of the barrel, although an alternative embodiments, the diameters may be made equal by cutting the threads to a smaller diameter relative to the barrel outside diameter.
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The disclosed configurations provide a relatively short overall rifle length and overall barrel length for a given length of usable bore. Because the breech cap does not extend into the bore, it allows the entire length of the bore to be used by the propellant and projectile, unlike conventional designs in which a breech plug is inserted to a significant depth within the bore, adding weight and reducing usable bore length.
While the above is discussed in terms of preferred and alternative embodiments, the invention is not intended to be so limited.
