Method of forming a chamber in a barrel blank

Abstract

A method of forming a chamber in a barrel blank has the steps of providing an elongated firearm barrel blank defining a bore and having a muzzle end and an opposed breech end, securing the blank in a fixture, determining a first reference location of the bore at a position proximate to the breech end, based on the first reference location, machining a first rough chamber bore at the breech end and along the bore to a selected depth, determining a second reference location of the bore at a position beyond the selected depth, and based on the second reference location, machining a second precision chamber bore. The fixture may be stationary during the steps of determining and machining. The step of determining a first reference location may include probing a surface of the bore and may include probing at least three different positions about the bore.

I claim: 
     
         1 . A method of forming a chamber in a barrel blank comprising:
 providing an elongated firearm barrel blank defining a bore and having a muzzle end and an opposed breech end;   securing the blank in a fixture;   determining a first reference location of the barrel blank at a position proximate to the breech end;   based on the reference location, machining a first rough chamber bore at the breech end and along the bore to a selected depth; determining a second reference location of the barrel blank at a position beyond the selected depth; and   based on the second reference location, machining a second precision chamber bore.   
     
     
         2 . The method of  claim 1  wherein the provided barrel blank is stationary during the steps of determining and machining. 
     
     
         3 . The method of  claim 1  wherein the step of determining a first reference location comprises probing a surface of the bore. 
     
     
         4 . The method of  claim 1  wherein the step of determining a first reference location includes probing at least two different positions about the bore. 
     
     
         5 . The method of  claim 1  wherein the provided barrel blank has a rifled bore with lands and grooves, and wherein the step of determining a first reference location includes probing a surface of a groove. 
     
     
         6 . The method of  claim 1  wherein the provided barrel blank has a rifled bore with lands and grooves, and wherein the step of determining a first reference location includes probing a surface of a land. 
     
     
         7 . The method of  claim 1  wherein the step of determining a first reference location comprises calculating a center of the bore. 
     
     
         8 . The method of  claim 7  wherein the step of machining a first rough chamber includes centering the first rough chamber on the determined first reference location. 
     
     
         9 . The method of  claim 1  wherein the blank has an outside surface at the breech end and wherein determining a reference location is irrespective of the outside surface. 
     
     
         10 . The method of  claim 1  including after determining a first reference location of the bore, rough machining an external barrel feature proximate the breech end. 
     
     
         11 . The method of  claim 10  wherein the external feature includes a barrel tenon. 
     
     
         12 . The method of  claim 1  wherein machining a second precision chamber bore includes maintaining the barrel blank stationary, and operating a machine tool having a moving cutting surface to form the chamber. 
     
     
         13 . The method of  claim 1  wherein machining a first rough chamber bore includes generating a rough chamber surface, and wherein machining a second precision chamber bore includes removing the entire rough chamber surface. 
     
     
         14 . The method of  claim 1  wherein determining a second reference location of the bore includes inserting a probe having an operational measuring tip, and having an elongated body portion having a diameter greater than the barrel blank bore.