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Rifles, Reloading, Optics, Equipment
Gunsmithing
Why dial a rifle bore within .0001"
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<blockquote data-quote="Pdvdh" data-source="post: 1142317" data-attributes="member: 4191"><p>Here's the methods of chambering and fitting a barrel Hired Gun describes on his website. Which leaves me wondering how J E Custom is rounding up barrel blanks with such little deviation from perfectly straight, chamber to muzzle?</p><p><a href="http://www.straightshootersupply.com/pricing.html" target="_blank">Pricing</a></p><p></p><p>"<em>Once passing quality control inspection your barrel is carefully mounted in the lathe. We dial in the barrel only on the end we are working on. When it's the chamber we dial two locations. The first one is right where the throat is to be located and then two inches farther in. All rifle barrels have a slight curve in the bore. The technology to drill a perfectly straight bore 30" deep is still too cost prohibitive for rifle barrels. Our goal is to get the chamber and throat perfectly aligned with the path of the bore. We use Starrett .0001" indicators with long reach styluses or Grizzly rods to reach up to 6" into the bore. We do not settle for .0002" variance as most shops do. We go the extra mile and keep dialing until the .0001" indicator is running dead zero. No detectable movement. Why go to this trouble? We do it because it is one of the many variables in a rifle we can control and eliminate.</em></p><p><em></em></p><p><em>Once dialed, the first thing is the position of the curve in the bore is notated and when the action threads are cut the curve of the bore is timed to torque up in the 12 o'clock position. If the curve is outside our limits the barrel is rejected. I can't reject any curve in the bore or we would be rejecting them all. We prefer to see this run out be no more than .020". Bartlein and Krieger are sometimes running less than .005" run out. </em></p><p><em></em></p><p><em>The threads are precision fit to your action and allow the tightest fit possible to your action. This precision fit is critical for the barrel action joint to behave as one under the pressures of firing. No CNC can match the fit we can achieve to your action. </em></p><p><em></em></p><p><em>Now the flush system is fired up to flush all machine swarf away from the cutting edges and out of the barrel during the internal machining operations. The chamber is roughed out to a depth equal to the shoulder of the cartridge and about .015"- .020" undersize. Then go in with an indexable tooled boring bar equipped with a carbide cutter. We then bring it to within .005"-.010" of final diameter. Then the precision chamber reamer is brought in and the chamber is cut to final size. Headspace is set with gauges from zero to plus .002" depending on the application and customer preference.</em></p><p><em></em></p><p><em>Once the chamber end is done the barrel is removed from the lathe and turned around to cut the crown and muzzle brake threads if so equipped. We use the same care to dial in the barrel for the crown and muzzle brake as we do the chamber. We dial in where the crown is to be and 2" back. We want that crown perfectly perpendicular to the actual bore. We cut super sharp 11 degree crowns.</em>"</p></blockquote><p></p>
[QUOTE="Pdvdh, post: 1142317, member: 4191"] Here's the methods of chambering and fitting a barrel Hired Gun describes on his website. Which leaves me wondering how J E Custom is rounding up barrel blanks with such little deviation from perfectly straight, chamber to muzzle? [url=http://www.straightshootersupply.com/pricing.html]Pricing[/url] "[I]Once passing quality control inspection your barrel is carefully mounted in the lathe. We dial in the barrel only on the end we are working on. When it's the chamber we dial two locations. The first one is right where the throat is to be located and then two inches farther in. All rifle barrels have a slight curve in the bore. The technology to drill a perfectly straight bore 30" deep is still too cost prohibitive for rifle barrels. Our goal is to get the chamber and throat perfectly aligned with the path of the bore. We use Starrett .0001" indicators with long reach styluses or Grizzly rods to reach up to 6" into the bore. We do not settle for .0002" variance as most shops do. We go the extra mile and keep dialing until the .0001" indicator is running dead zero. No detectable movement. Why go to this trouble? We do it because it is one of the many variables in a rifle we can control and eliminate. Once dialed, the first thing is the position of the curve in the bore is notated and when the action threads are cut the curve of the bore is timed to torque up in the 12 o'clock position. If the curve is outside our limits the barrel is rejected. I can't reject any curve in the bore or we would be rejecting them all. We prefer to see this run out be no more than .020". Bartlein and Krieger are sometimes running less than .005" run out. The threads are precision fit to your action and allow the tightest fit possible to your action. This precision fit is critical for the barrel action joint to behave as one under the pressures of firing. No CNC can match the fit we can achieve to your action. Now the flush system is fired up to flush all machine swarf away from the cutting edges and out of the barrel during the internal machining operations. The chamber is roughed out to a depth equal to the shoulder of the cartridge and about .015"- .020" undersize. Then go in with an indexable tooled boring bar equipped with a carbide cutter. We then bring it to within .005"-.010" of final diameter. Then the precision chamber reamer is brought in and the chamber is cut to final size. Headspace is set with gauges from zero to plus .002" depending on the application and customer preference. Once the chamber end is done the barrel is removed from the lathe and turned around to cut the crown and muzzle brake threads if so equipped. We use the same care to dial in the barrel for the crown and muzzle brake as we do the chamber. We dial in where the crown is to be and 2" back. We want that crown perfectly perpendicular to the actual bore. We cut super sharp 11 degree crowns.[/I]" [/QUOTE]
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Why dial a rifle bore within .0001"
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