R
Riflemeister
Guest
I've been working on a Win 70, 280 AI for a customer and have run into a problem I don't see any way out of.
I set the barrel up through the headstock with a copper wire ring on the breech end and a 4 screw spider on the back end. I dialed in both ends with a dial indicator in the bore to run true on both ends and faced the breech end. I lapped the burrs from the bore and fitted a pilot on a range rod. Using two .0001" indicators, one next to the barrel, and one at the end of the range rod, I got them both running less than .0001". Checking the muzzle end of the blank, it was running .086" TIR. That is nearly double my previous high reading. I figured that was why I used the range rods and proceeded to cut metal.
Using my Gretan barrel flush and JGS floating reamer holder and a close fitting pilot, I cut a chamber .500" short of full depth. I removed the flush system, cleaned the barrel and checked chamber runout and borescoped the throat. Everything was concentric and the throat looked very even on the lands and grooves.
Satisfied, I turned, threaded and indexed the barrel so the high side was up.
I then set up the flush and proceeded to cut the chamber to minimum headspace. After .200", I stopped the lathe and backed the tailstock out .010" and attempted to move the tailstock out to clean the reamer and check the chamber. The tailstock would not withdraw until I backed it out .050". The binding of the reamer in the chamber continued as I finished the chamber to depth.
After cleanup, I borescoped the chamber and the throat was noticeably off toward the side away from the direction the bore ran out. It is like the reamer ran straight and the curve in the bore was run into by the reamer throat. Runout of the chamber is still near zero. I figure the binding while trying to remove the reamer from the chamber was the pilot trying to follow the bore runout and binding in the bore.
I called Dan Lilja to discuss the bore runout and he said the throat cutting eccentric was a common problem with the JGS reamer holder. The only problem encountered previously with the JGS holder was fluting a chamber when it got out of adjustment and developed end float. Anyhow, Dan says that excessive bore runout would not cause the problem and I need to junk the reamer holder I've used for 15 plus years.
Anyone encountered .086" or greater runout using range rods to set up through the headstock? If so, how did it work out? How much bore runout would you attempt to chamber? From the way things looked at .500" short, I probably could have cut a good 7mm-08 chamber in that barrel.
There is not enough blank ( #4 contour) to start over, so I called Hart and ordered a new blank today. Some days just suck!
I set the barrel up through the headstock with a copper wire ring on the breech end and a 4 screw spider on the back end. I dialed in both ends with a dial indicator in the bore to run true on both ends and faced the breech end. I lapped the burrs from the bore and fitted a pilot on a range rod. Using two .0001" indicators, one next to the barrel, and one at the end of the range rod, I got them both running less than .0001". Checking the muzzle end of the blank, it was running .086" TIR. That is nearly double my previous high reading. I figured that was why I used the range rods and proceeded to cut metal.
Using my Gretan barrel flush and JGS floating reamer holder and a close fitting pilot, I cut a chamber .500" short of full depth. I removed the flush system, cleaned the barrel and checked chamber runout and borescoped the throat. Everything was concentric and the throat looked very even on the lands and grooves.
Satisfied, I turned, threaded and indexed the barrel so the high side was up.
I then set up the flush and proceeded to cut the chamber to minimum headspace. After .200", I stopped the lathe and backed the tailstock out .010" and attempted to move the tailstock out to clean the reamer and check the chamber. The tailstock would not withdraw until I backed it out .050". The binding of the reamer in the chamber continued as I finished the chamber to depth.
After cleanup, I borescoped the chamber and the throat was noticeably off toward the side away from the direction the bore ran out. It is like the reamer ran straight and the curve in the bore was run into by the reamer throat. Runout of the chamber is still near zero. I figure the binding while trying to remove the reamer from the chamber was the pilot trying to follow the bore runout and binding in the bore.
I called Dan Lilja to discuss the bore runout and he said the throat cutting eccentric was a common problem with the JGS reamer holder. The only problem encountered previously with the JGS holder was fluting a chamber when it got out of adjustment and developed end float. Anyhow, Dan says that excessive bore runout would not cause the problem and I need to junk the reamer holder I've used for 15 plus years.
Anyone encountered .086" or greater runout using range rods to set up through the headstock? If so, how did it work out? How much bore runout would you attempt to chamber? From the way things looked at .500" short, I probably could have cut a good 7mm-08 chamber in that barrel.
There is not enough blank ( #4 contour) to start over, so I called Hart and ordered a new blank today. Some days just suck!