How much bore runout is too much?

[Riflemeister]

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!

 

[wnroscoe]

I've gotten away from using the copper wire in my jaws to hold the barrel. I found it can allow the barrel to move or slip undetected. This may have very well happened to you. I now use small copper shims between the barrel and jaws and have had good luck with that method.

I also check my barrel several times during the process to insure nothing moves unexpectedly. FWIW, I turn down my tennon, thread and cut the bolt nose counter bore prior to chambering. I always re-check the barrel prior to chambering to make sure it didnt move during the initial process. If any adjustments are needed as far as indicating the barrel I simply touch the barrel shoulder with my tool to make a very slight cut to insure it's still running true to the bore.

Good luck with the second barrel.

 

[jackie schmidt]

Riflemeister

I don't chamber the way you do, but it appears that what you encountered was a pretty bad "runnout spot" right up in there where your throat was forming. I hate it when this happens, but it is not that uncommon.

I would assume that when using that range rod to indicate the bore, you do insert it in at least as long as the case, preferrably a little longer. That way, at least the part of the barrel that your reamer "sees" will be running true. If, for instance, you just indicate a 3 inch length, and the reamer goes in further and encounters a bad spot, you are out of luck.

Of course, as you know, you are at the mercy of what ever runnout exist in the rest of the barrel as to how much the muzzle will run out. That is simply a product of truing barrels this way.

Ab gave some good advice. Do all of the roughing work before ever finishing anything. That way, you have a less chance of any movement in your set-up. This is just good machine shop practice.

It is not a bad idea to periodically check things. Most barrel set-ups are not that stout, a little too much aggresion with a tool can cause things to move.

Incidentally, how dull is that reamer. Usually, any binding will cause an oversized chamber, unless the flutes are so dull that the bind does not induce cutting. This is usually what happens when a reamer with a snugg fitting pilot encounters a severe runnout spot in a barrel. The pilot will try to follow the runnout, but since the reamer won't bend, it just cuts oversize......jackie

 

[Bnhpr]

Riflemeister,

I indicated a .257 shilen barrel with a range rod and the muzzle was wobbling terrible. I did not measure it, but it was .050" at least. I re-indicated it, at the throat and muzzle, drilled and bored it, and chambered it 257 Roberts, and it shoots fine. I've given up on the range rod since.

Sacrifice the angle for less runout.

Ben

 

[JerrySharrett]

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.
There is not enough blank ( #4 contour) to start over, so I called Hart and ordered a new blank today. Some days just suck!

How many times? How many times?? Indicating off the extension of a range rod is just asking for trouble. Using a floating reamer holder like those sold for gunsmith use can contribute to the problem as well as cause other problems itself like oversized chamber and/or chamber out of round.

On top of all that, if the barrel shoots at all it probably will have to be indexed!!

 

[JerrySharrett]

I turned, threaded and indexed the barrel so the high side was up.

Some days just suck!

Please explain how you did this on a conventional lathe with leade screw and half-nut. We all might learn something here.

 

[Riflemeister]

Indexing barrel thread

Jerry,
To index the barrel thread, I screw an old cutoff barrel stub into the action and mark the top of it. I then use calipers to measure from the torque shoulder to top of the thread at the top. On the barrel in the lathe, I turn it to dimension and paint with Dichem. At the muzzle end I measure the the point of furthest excursion with a dial indicator and mark .001" before and after to account for indicator dwell and halfway in between is the point I want to be up. Using a TDC finder I place the muzzle in the up position and then mark the dichemed stub at the 12 o'clock position. Using a machinists rule and sharp scribe, I scribe a fore and aft line at TDC. I then use the caliper to mark a cross line using the dimension I got from the action except I subtract .010" to insure I don't go past. I set the compound at 29 degrees and set my threading tool with the fish. I set my cross slide handle at 9 o'clock so I always make the same motion to lift the threading tool.

Setting the point of the threading tool to hit the scribed target is a matter of trial and error. I will engage the half nut and turn the lathe by hand until I can screw in the compound and touch the fore and aft line with the tool. If it is not on target, and it seldom is, I place the gear engagement in neutral and rotate the lathe by hand about 10-15 degrees and re-engage the gears. I then disengage the half nut, back the carriage out and rotating by hand, re-engage the half nut and try again. Usually within 5 or 6 tries, I can have the point of the tool hitting the target as close as I can get it. I then set my threading indicator at "1".

I then cut the thread a to a smooth running fit and try the action on the stub. If I have done everything correctly, it usually turns on with hand tightening to 25 to 30 degrees before TDC. I then calculate the cut required on the torque shoulder to get it to 10 degrees before TDC to allow for tightening with the wrench and barrel vise and make several small cuts sneaking up and checking to get as close to 10 degrees before TDC for a 16 pitch thread as I can get. I measure the angle from a scope base attached to the action with a protractor with a bubble level.

When finished, I'm confident I have done everything within my capability to pace the high side of the barrel in the proper place. I hope that helps with your machining Jerry.

 

[JerrySharrett]

. I hope that helps with your machining Jerry.

Thanks. That is quite an impressive exercise but it is not necessary. If you will just dial in the muzzle and chamber throat area then prebore the chamber body to close to finish size you will have a chambered barrel that 1) does not need indexing, 2) shoots where you point it (i.e. in a straight line from the action/bolt centerline-very important for proper tracking), and 3) a chamber where the intersection of the throat and barrel bore perfectly intersect.

 

[Riflemeister]

Indicating chamber throat

Jerry,
I have a couple of questions on indicating the chamber throat.
1. what indicator are you using to get to the throat area of a 7mm STW or 338 Lapua mag?
2. Doesn't a long stylus attached to an indicator change the accuracy of the reading? Quadruple the length and make a .0001" indicator a .0004" accuracy indicator?

 

[Dave Short]

Thanks. That is quite an impressive exercise but it is not necessary. If you will just dial in the muzzle and chamber throat area then prebore the chamber body to close to finish size you will have a chambered barrel that 1) does not need indexing, 2) shoots where you point it (i.e. in a straight line from the action/bolt centerline-very important for proper tracking), and 3) a chamber where the intersection of the throat and barrel bore perfectly intersect.

Jerry, you just summed up what many of us have been saying forever. If you succeed in finally getting it across, Deltronic (it's a COMPANY, not a type of pin) will have to rent out part of their building to someone. I think most of us have observed that, when set back (random "index") a great barrel still shoots....and a tomato stake stays a tomato stake. We also have observed that barrels set up directly off of both ends of the bore shoot within a few inches of one another on the same rifle.

-Dave-

 

[mike in co]

Jerry,
I have a couple of questions on indicating the chamber throat.
1. what indicator are you using to get to the throat area of a 7mm STW or 338 Lapua mag?
2. Doesn't a long stylus attached to an indicator change the accuracy of the reading? Quadruple the length and make a .0001" indicator a .0004" accuracy indicator?

several options

do a search on indicators....
by pre boring you can get in further
and there is the 2.5 indicator which is .0005 easy to "see" less than that.

go read jackie's method of setting up to chamber. spyder works best with a muzzle that has been dialed in on the headstock and crowned first.

just 2 cents from a beginer....

who would you rather learn from:

a person that was taught to use a lathe to be a gunsmith,
or
a machinist that uses his work skills to chamber benchrest bbls ?

( this is not meant to be a slam on gunsmiths, but who has the better lathe skills/knowledge. i have some machine background, i listen when jackie speaks about chambering).


mike in co

 

[JerrySharrett]

Jerry,
I have a couple of questions on indicating the chamber throat.
1. what indicator are you using to get to the throat area of a 7mm STW or 338 Lapua mag?
2. Doesn't a long stylus attached to an indicator change the accuracy of the reading? Quadruple the length and make a .0001" indicator a .0004" accuracy indicator?

I use a 1.5" dial Interapid indicator graduated in 0.0001" increments and a 2.75" and 5.5" styluses from www.longislandindicator.com . Yes the longer stylii do cause a measurement error but you are not concerned with the AMOUNT of runout, you are just concerned if there is ANY runout. If you get no movement on an indicator like the Interapid then you are pretty certain you are close enough.

http://longislandindicator.com/p21.html then scroll down the page. Notice what these folks say about Chinese X-Test vs Interapid.

 

[Bnhpr]

Jerry,
I have a couple of questions on indicating the chamber throat.
1. what indicator are you using to get to the throat area of a 7mm STW or 338 Lapua mag?
2. Doesn't a long stylus attached to an indicator change the accuracy of the reading? Quadruple the length and make a .0001" indicator a .0004" accuracy indicator?

It is improbable that the bore shifts a measurable distance over 1/2" that you can't reach with a indicator....on the magnum length cases.

It is extremely probable that a range rod is not coaxial with the bore at the throat....since your indicators are 3 and {x} inches away from the place we all agree that matters (throat)....and your problem above supports that.

I have been using the long stylus, and agree their is dilution, but..the needle still moves a needles width when the tip moves .0001...so I strive for a dead needle. As a note....Butch talked me into a Mitutoyo that I can direct indicate to .0001 with....on it's way for x-mas...

I'm a marine/mechanical engineer, that grew up in a machine shop, and loves to work on a lathe and shoot....I built my first cannon on a leblond lathe when I was 12 years old.......so building rifles is something that I do to relax...

Very interesting topic this is...

 

[jackie schmidt]

It Makes No Difference...........

how you chamber. You can carve it in there with a coal chisel.

But, what DOES matter is the results.

How many of you actually check your final barrel work to see just how well things really come out.

You have several areas that should be truly straight and square with each other.

Before you take the barrel out of the lathe after the final operation, do this.

Reach in with your long stylus and indicate the lands just aft of where the reamer stops cutting. Then, move it back and check the actual lead. Then, indicate each end of the chamber, from the neck to the big end. Then, indicate the face of the tenon where it butts against the action. Finally, kick the half nut in, take up the slack in the carriage, and place the indicator stylus between the V's of the thread, just like you were re-catching the thread lead. Roll the chuck by hand, being carefull to keep the slack one way.

All of these readings should be no more than .0003-,0004 out with another. The face of the action should be "zero"with the threads.

If you find discrepencies, and you are doing Benchrest Quality Chambering, then you might need to trouble shoot your set-up.........jackie

 

[Dennis Sorensen]

On longer chambers that I can not reach the throat area of the barrel with an indicator I use a tight fitting Deltronic pin inserted into the throat area and measure run out at the very end of it and about 1/2 inch in from the end.

In this particular case the run out at both locations showed no run out within a 10 thousands of an inch. They usually don't dial in that perfect... lucky on this one...

This remained the same before and after machining the threads, the shoulder and the bolt nose recess.

I will now bore the chamber and then use a reamer and when finished check the chamber run out... it usually is less than .0002.
... I have finished and in this set up I can not measure any run out at the rear of the case... This is as good of a result as I have ever had... usually a ten thou or two is about it...

Then the barrel will be removed from the lathe....

...inspecting the throat area it appears very uniform and centered on the bore...

 

[Bnhpr]

How many of you actually check your final barrel work to see just how well things really come out.

I do.....

At the bench......as you say, the results are what really matter.

Although I agree runout is a more quantifiable check of the chambering job...

Ben

 

[JerrySharrett]

I do.....

At the bench......as you say, the results are what really matter.

Although I agree runout is a more quantifiable check of the chambering job...

Ben

Jackie is very correct, check the critical surfaces as to their runout relationship to each other, especially chamber surfaces and their relationship to the tenon shoulder.

After checking these surfaces with a high quality dial indicator of high resolution, if anything was running out, I'd seriously troubleshoot my setup at that time, not later.

If you did not check and the barrel did not shoot well, then what? Would you know if it was the load, the bullets, the bullet jam, etc.., the shooter, the setup.....see where I am going?? Whereas, if you KNOW the critical surfaces are true with each other, then you can stay at the range and work on the other factors that affect tune.

 

[Jeffrey]

These runout posts are very interesting reading. There seems to be two perspectives on setting up the barrel for cambering that include indicating the muzzle and breech end to run with each other, somewhat the same as between centers, and the other one being setting the chamber end bore straight without regard to the muzzle runout. Does anyone change their method depending on the amount of bore curve found in the barrel?

If there is a significant curve to the bore and you set the "ends" to run together, and then indicate 0-0 at the throat location of the chamber end, are you guaranteeing yourself some chamber misalignment. After all, the pilot for the reamer is beyond the throat location when the throat is being cut. If you have only indicated the bore at the throat location then that's the only point the the bore will run true. Pre-boring will keep the reamer straight as long as it doesn't have to fight with the pilot too much.

Indicating the ends of the barrel to each other will keep the barrel located in the stock channel better, but is the bullet really aligned with the bore in the best way when the round is chambered. I know it won't be off much, but it will be off depending on the amount of curve in the barrel.

Using a range rod to set the chamber end bore straight can be done fairly accurately depending on how "round" the bore is and how closely you ground you rod. Using a rod purchased rod from PTG having a good fit on the pilot and a slow taper can also be reasonably accurate.

My biggest problem is rechambering when there isn't enough length to cut the whole tenon off and start over. Everything is a compromise at that point. The threads have to be extended and kept concentric with the original threads while the chamber is running out .004 to .005. Now you have to straighten the chamber out to the bore. I have seen chambers cut with the "end to end" alignment and from those who just use the O.D. of the barrel for alignment, where the side of the bullet actually gets shaved by the throat while the concentricity of the loaded rounds showed within .002.

Each to his own method as they will both work depending on the amount of bore curve, but I think there needs to be an evaluation of how much curve is in the bore your dealing with before you settle on the best way to go. But then again if the barrel curve is that bad maybe it should become a "jack handle".

As far as testing the result of your work ,I did one barrel where the shooter has come within one point on three different occasions of breaking the national record at 600 yards, 900 yards and 1000 yards . . . is it the chamber or the shooter? Of course I think it's the shooter.

Jeff

 

[JerrySharrett]

These runout posts are very interesting reading. There seems to be two perspectives on setting up the barrel for cambering that include indicating the muzzle and breech end to run with each other, somewhat the same as between centers, and the other one being setting the chamber end bore straight without regard to the muzzle runout. Does anyone change their method depending on the amount of bore curve found in the barrel? If the curve is very great, I'd send the barrel back

If there is a significant curve to the bore and you set the "ends" to run together, and then indicate 0-0 at the throat location of the chamber end, are you guaranteeing yourself some chamber misalignment. After all, the pilot for the reamer is beyond the throat location when the throat is being cut. If you have only indicated the bore at the throat location then that's the only point the the bore will run true. Pre-boring will keep the reamer straight as long as it doesn't have to fight with the pilot too much. If you have aligned the throat area, predrilled and prebored, and used a snug fitting pilot bushing, and are using a HSS or HSS/CO reamer, the chamber transition will be concentric. While all bores are curved, the gun drill and bore reamer will not allow a steep curve over a short distance.

Indicating the ends of the barrel to each other will keep the barrel located in the stock channel better, but is the bullet really aligned with the bore in the best way when the round is chambered. I know it won't be off much, but it will be off depending on the amount of curve in the barrel. Don't worry about how the barrel OD fits the stock channel. Be concerned where the muzzle exit points in relation to where the stock/action points.

Using a range rod to set the chamber end bore straight can be done fairly accurately depending on how "round" the bore is and how closely you ground you rod. Using a rod purchased rod from PTG having a good fit on the pilot and a slow taper can also be reasonably accurate.

My biggest problem is rechambering when there isn't enough length to cut the whole tenon off and start over. Everything is a compromise at that point. The threads have to be extended and kept concentric with the original threads while the chamber is running out .004 to .005. Now you have to straighten the chamber out to the bore. I have seen chambers cut with the "end to end" alignment and from those who just use the O.D. of the barrel for alignment, where the side of the bullet actually gets shaved by the throat while the concentricity of the loaded rounds showed within .002. If you have determined you have a reasonably straight bore, and you have set the barrel up as described above, you will not have that problem!!

Each to his own method as they will both work depending on the amount of bore curve, but I think there needs to be an evaluation of how much curve is in the bore your dealing with before you settle on the best way to go. But then again if the barrel curve is that bad maybe it should become a "jack handle". How are you going to quantify too much curve? In actuallity, a curved bore can shoot just as well as a reasonably straight one, if it is fitted properly.

As far as testing the result of your work ,I did one barrel where the shooter has come within one point on three different occasions of breaking the national record at 600 yards, 900 yards and 1000 yards . . . is it the chamber or the shooter? Of course I think it's the shooter. It doesn't matter who the shooter is, if the barrel will not shoot up to winning standards, the shooter looses!!

Jeff

.....

 

[Butch Lambert]

Jeff,
If you set the barrel back why would you need to add threads. Indicate the old chamber and shoulder in and just cut a longer relief. Losing a couple threads setting one back ain't gonna hurt nothing. Take your PTG or other range rod and indicate it in. Take it out and reinsert it and check your indication. I bet it runs out at least .001. That right Ben?
Butch