Breech Adjustment Tool

About:  A standard muzzle loading gunsmithing task is adjusting or fitting a breech plug. However, if you need to shorten the engagement of an existing plug to adjust the fit between the shoulder and the breech plug face, holding a part with no square or parallel surfaces is always difficult.  This tool allows the plug to be held and worked in either a lathe or a vise without difficulty.

Specifications:  Mild steel hexagonal body with two clamp screws and six clamp screw positions.  Additional clamp screw for fine adjustment.  Please specify breech plug thread diameter and pitch.

Details:  Every once in a while, I need to re-breech a barrel or fit up a new breech plug to an existing barrel.  If you make a new plug from scratch by machining it out of a piece of bar stock on a lathe, you can get the plug bottomed out correctly before you remove all the rest of the material to form the tang.  However, if you need to shorten the engagement of an already formed plug to adjust the fit between the shoulder and the breech plug face, holding a part with no square or parallel surfaces is nearly impossible.

This tool is a hollow steel cup with a closed end.  The closed end has a threaded hole to match the breech plug.  It also has six, ¼ -28 drilled and tapped holes through each face of the hexagonal body for two clamp screws that hold the plug firmly in place.  The tools are available in all the currently used breech plug thread sizes. 

The hexagonal body allows additional clamp screw holes for a little more flexibility in where you can position the plug and makes the tool handy to hold in either the bench vise or a three jaw lathe chuck. For use without a lathe, the added 8-32 screw shown near the edge of the tool allows fine adjustment of the plug position.  This screw is fitted with a nylon shoe to prevent damaging the breech plug threads and is used to clamp the plug for facing with a file. 

If the face is to be filed, the plug is screwed into the tool and a standard washer is placed over the protruding end of the plug.  (The washer will protect the face of the tool, not dull a file, and is easily replaced as necessary.) The plug position is adjusted until just the length to be removed protrudes above the washer.  The 8-32 clamp screw is then used to hold the plug in position and the extra plug length is filed off flush and square with the washer / tool face.

 

Price:

  • Breech Tool for 9/16-18 plug $48
  • Breech Tool for 5/8-18 plug  $48
  • Breech Tool for ¾-16-18 plug  $48

Breech Adjustment Tool

 

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