? chucking up a barrel ?

[JerrySharrett]

Since you are running a dial indicator point on lands and grooves, you can get it as close as you can, but when you check on the neck of the chamber when you get close to finishing the chamber, it's easier to get the neck dialed in if you didn't quite get it right when you indicated on the lands and grooves.

.

If the finish location of the chamber neck is dialed in exactly, and the chamber body portion is drilled and bored true with that setting (leaving enough "meat" for the reamer to finish the body portion), the reamer body will be guided by that bored hole and the reamer neck/leade portion will be guided by a snug fitting reamer bushing. The result is that you will have a chamber that is exactly concentric to the barrel bore at the point where the bullet enters the bore.

 

[Greg Walley]

bore orientation at the muzzle

By the time I am chambering the breech end, I have already cut the barrel blank off to finish length plus about 3/8-1/2 inches of finish length.

I use Dan Liljas BASIC program to establish barrel weight and length for where I want it to finish. For 100/200 barrels I use the Bruno Medium blank which is 29" long. By shifting the cut off points I can get a 22" barrel that is anywhere from about 4# 5 oz to 5# 5oz. This allows me to indicate the muzzle (outboard) end at point that is 1/2" or less of the finishing place for the muzzle.

Jerry,

I'm curious, how far out of center (on average) is the hole at the muzzle when you are finished chambering your blanks? Approximately how much do you remove from the muzzle end of the barrel to finish your blanks?

Is your POI relatively close from barrel to barrel?

Some of the threads that I've read in this forum have me questioning the methodology used to chamber barrels. I would suspect a barrel would have to be way out of axial alignment or not perpendicular with the receiver for it to print a foot off at 100 yards...or the hole in the muzzle is way out of center.

Just an FYI...I try to use blanks of the correct taper so I can remove a minimal amount from the muzzle end to keep the hole as close to the center as possible. At least there is a better chance of the hole being centered closer to the end of a blank.

 

[JerrySharrett]

Jerry,

I'm curious, how far out of center (on average) is the hole at the muzzle when you are finished chambering your blanks? Approximately how much do you remove from the muzzle end of the barrel to finish your blanks?

Is your POI relatively close from barrel to barrel?


.

You back from Italy already??

As to out-of center at the muzzle. On the Bruno Mediums I use for Panda action/Leonard stock/Leupold scope guns. I cut about 7" off the muzzle end. Then I put a pin gage in the hole and indicate that pin while dialing in the chamber end. The last 2-3 years the OD is out of concentricity with that pin by about 0.007"-0.010". But, realize, the muzzle bore is dialed in with the chamber neck/body/tenon/tenon shoulder.

Remember in dialing in a barrel simultaneously at both ends, the most curve is about half way between.



When I remove a zeroed barrel I cambered and screw another on, the POI will easily be within 2" at 100 yards. That includes sliding the scope and mounts off the Panda integral rail to eliminate side shock to the scope.

Edit #2-this is why I think it is important to have a lathe that has a short headstock that allows working both ends of a benchrest length barrel at the same time. The barrel in the above photo is 22" long and there is about 2-1/4" extending from the chuck jaws at the inboard end. I can easily work a barrel down to 18 1/2" on both ends.

 

[frwillia]

When you use a full length blank, both ends of the bore are belled slightly from lapping. If you use any of the belled end for dialing in the barrel, you are getting a false reading. The muzzle end isn't that critical, but if it's off much, it may be hard to get the barrel to zero when you start shooting it.

Yup. I cut at least an inch off each end in the band saw before I start.

With using an indicator to dial in the barrel at the projected throat of the chamber, I'm just picking that point as the most important place for the barrel to be indicated.

Agreed.

I don't use a long arm on a DTI, I use the Grizzly rod stuck in to where the throat will be, which, with a fitted pilot, is arguably every bit as good as a 1-1/2" (or longer, the last chamber I did was a .30-06 which would have required a 2-3/4" arm on the DTI) arm on a DTI. But we agree at least conceptually, if the chamber is to be done right, the throat reigon is the place that needs to be centered from the beginning.

With drilling and boring out the chamber end any belling is done away with by the chamber. Since you are running a dial indicator point on lands and grooves, you can get it as close as you can, but when you check on the neck of the chamber when you get close to finishing the chamber, it's easier to get the neck dialed in if you didn't quite get it right when you indicated on the lands and grooves.

OK, the benefit of that tweak after the reamer is almost done, that's what's confusing me. In my mind, the last time one can check the run out at the throat, and have adjustments make any difference at all in the relationship between the chamber and the bore, is just before one finishes the pre-boring with the boring bar. If the adjustment (tweak) is less than the amount of material remaining to be removed by the boring bar, it will make a difference because the prebored hole can still be machined concentric to the tweaked throat location.

Once the pre-bore is completed, chambering is started, and the reamer pilot is in the bore, nothing from then on will make any difference in where the reamer is going. In other words, assume that just before one finishes the chamber, one indicates the throat and finds it is moving in a 0.001" diameter circle. If my understanding of the physics governing reamer behavior is right, the reamer is already totally committed to the chamber, pilot is in the bore, so if the chuck is tweaked to center it, nothing changes - the reamer goes to exactly where it was going to go originally before the tweaking took place. The reamers path, and the chambers orientation is set by how the bore is indicated when it is prebored. Once the pre-bore is done, the reamer is going to go where it is pointed by the prebore and the pilot in the bore. In fact, it looks to me like the reamer is going to go to the exact same place even if one takes the barrel out of the headstock and finishes the chamber by hand, which is a heck of a "tweak".

This makes my head hurt, but the only difference I can see from the final tweak as described is that the tenon's concentricity with the chamber may be improved since it hasn't been turned to final diameter or threaded yet. If the tweak is as small as it should be using your process (from your web page), probably .001 or less, maybe a lot less, I don't see that change in tenon concentricity making any difference in how the barrel groups. It might change the zero a click or two at 100 yards, but that is no big deal. In other words, once the reaming has started, the next time a measurement has an effect is after the chamber is finished when one can make the adjustment that might slightly improve the tenon's concentricity with the chamber.

Just remember no matter how you go about getting your chamber, the final word to how good a job was done is how the barrel shoots on paper. Probably a lot of what we do as gunsmiths when setting up a barrel, probably only has an effect between our ears. Do a bad job though and you'll find out about it as the barrel won't shoot.

Roger that!

Fitch

 

[Jim Borden]

2 points connected for a straight line

The only thing that puzzles me about just indicating the throat area where the reamer will make the throat is what second point is being used to establish the line that you want to be coaxial with your lathe?. Merely indicating the throat contact point does not mean that the axis of the reamer will be coaxial with the axis of the barrel and of the lathe. A second point is required in the rifling as another point to be bucked in to make the bore of the barrel coincide with the axis of the lathe and axis of the reamer.

That is why a pusher with float (a form of floating reamer holder) helps insure that the throat on the reamer is actually aligned with the bore of the barrel (snug busing to bore and good bushing to reamer spindle required). I have seen chambers that were indicated in a person's lathe at .00005 TIR --but, since the chamber was primarily cnc cut and then chased with a reamer it does not mean that the axis of the chamber was within .00005 of the bore of the barrel.

If a barrel is indicated in at the throat within .0002 TIR and then the chamber is machined by taper boring or by cnc machining and then chased with a reamer and the rear and shoulder do not run out .0002, then the axis of the chamber by definition is not aligned with the axis of that barrel's bore. Furthermore, as described above, if the throat is not indicated and aligned in at least two places along its length, there is no basis to believe that the barrel is actually indicated in to be coaxial with the spindle bore.

Just make a sketch and see if you can picture what I am describing.

Jim

 

[Mike Bryant]

I indicate at two points, the muzzle end and the projected throat. I use Deltronics pins to do the initial indication on each end of the barrel and then use the indicator point at the projected throat to finish indicating the barrel in. To be fair, I haven't tried the Gritter's method of using a range rod and moving the muzzle end around to get a range rod to indicate in at two points on the range rod. That's about the only way I haven't tried. I don't have the long range rod and don't see the need to buy it. As I've said before on the subject of chambering barrels, there's more than one way to skin a cat when it comes to chambering a barrel. Doesn't mean one method is right and everything else is wrong, just different.

 

[jackie schmidt]

Try This

Forget about the "Gunsmith" thing for a minute and look at this strictly from a Machinist viewpoint.

If bores were truely straight, all of this would be a moot point, because any 1st year apprentice can indicte two points.

Since bores are not "straight", (in fact, they are not even "curved', they have "kinks" in them), you have no choice but to true two points and then some way get a third point running true with those thwo points. From a machinist standpoint, the only way to do this is to single point bore that "third point", thus establishing three points that run dead true with the machines bearings, (ie, "true").

By establishing the muzzle end true, and then establishing a point in the bore's area that will represent the first thing that the bullet "sees" as it leaves the case neck, then single point boring the chamber so it runs dead true with these two points, you will have no problem establishing a chamber that is "true" with the barrel's ID. That is, true with the originol two indicated points, heck, one inch further from those two points may show as much as .001 runnout. There is nothing you can do about this, because the bore is not even straight with it's own self.

How many of you actually check everything after you finish a chamber. I do. I have written this before, but for those that have not been around that long, I will repeat the proccess.

After you have finished your entire chamber job, and before you remove the barrel from the final set-up, here is how you check your work.

Take your long stylus indicator and reach into the bore just a fraction further than where the lead angle ends. Indicate the lands and grooves, and see how much variation you get. Then, move the indicator back untill you are on the actual tapered lead, (the last thing the reamer cut). Take a reading. Then, move the indicator back to the neck portion of the chamber, then to the body of the chamber, fornt and back.

Then, put your lathe in what ever thread you cut, and kick the half nut in. Place the ball stylus of the indicator in the V's of the thread, roll the chuck untill all slack is out and the carriage is advancing. Record the indicator reading. Then place the stylus on the shoulder of the tenon, and record any runnout there.

If you get more than .0002 to .0003 on any of these, you are inducing runnout somewhere in your set-up. And, untill you actually check your work, and see, you are simply relying on your set-up to be correct.

Of course, I am well aware that many of the lathes that Gunsmiths and Hobbyist use for their work are not even capable of producing this type of accuracy. Which leads us to this point. How accurate does all of this have to be. I have checked barrels done by others, and in my opinion, they never actually check their finished job because I get quite a bit of runnout when checking the various fits against the others. These barrels shot great.

Sorry, but I tend to look at everything from a Machinist viewpoint. In my world, the only thing that counts is the finished job. Of course, you do have to have a means of performing operations that are within the capabilities of your shop, and of course, your budget And, you have to be willing to check your set-ups and correct any procedures that will cause the finished piece to be less than satisfactory when subjected to final inspection.

In my opinion, many of our "gunsmiths", and "machinist" in general, are simply "painting by the numbers". Change any part of the equation, and they have no way of knowing how to modify the operation to correct the flaws that can show up in the final inspection........jackie

 

[eww1350]

Great discussion...makes one think about setup and alignment...we have yet to determine if a properly set up barrel (indicated at the muzzle end and the throat) will shoot better or worse than a barrel indicated using the Goordy Gritters method...it would be interesting to chamber a 6ppc or 30BR using one method...shoot it (about 50 shots max) then set it up and rechamber it using the other method then shoot it using the same action,stock,load,shooter and place...to see if the barrel shows a significant change...

 

[frwillia]

Since bores are not "straight", (in fact, they are not even "curved', they have "kinks" in them), you have no choice but to true two points and then some way get a third point running true with those thwo points. From a machinist standpoint, the only way to do this is to single point bore that "third point", thus establishing three points that run dead true with the machines bearings, (ie, "true").

Exactly. One picks two points on the basis that a straight line between them is the best approximation of the bore for purposes of maximizing accuracy, then single point bores to make the chamber coaxial with the straight line between those two points. The problem is in the assumption, and it is an assumption, that only two pionts can be picked and in the assumption that a point near the muzzle and a point near the throat are "always" the best representation of the true bore axis of the barrel and will result in maximum acuracy chambers and crowns.

As I understand it, the two points of critical interface for the bullet with the bore are where it enters it at the throat and where it leaves it at the muzzle. So, what two points best represent the bore axis of interest at the chamber throat? What two points best represent the axis of the bore at the muzzle? Given that the bore is kinked and wanders around randomly inside the barrel, what are the chances it is always the same two points, one near the muzzle, one near the throat? In my opinion, while the chance is not zero, it is so close to zero that the difference doesn't matter.

On the other hand, it may not matter when one gets to the range and starts shooting.

The other consideration is that one can really choose 4 points in the barrel, two near the throat, two near the muzzle. The two near the throat can be used to align for chambering, the two near the throat can be used to align for cutting the crown. That is in essence what Gordy does, which most of you already know.

The only down side to Gordy's approach is the need to index the barrel to point the bullets exit path as close to in the vertical plane as is practical, which is so easy to do even a novice like myself was able to do it on my very first barrel (which was a Savage with barrel nut - a tenon with shoulder would have been even easier). Other than that, it's really no harder to do.

By establishing the muzzle end true, and then establishing a point in the bore's area that will represent the first thing that the bullet "sees" as it leaves the case neck, then single point boring the chamber so it runs dead true with these two points, you will have no problem establishing a chamber that is "true" with the barrel's ID. That is, true with the originol two indicated points, heck, one inch further from those two points may show as much as .001 runnout. There is nothing you can do about this, because the bore is not even straight with it's own self.

I respectfully disagree with your conclusion there is nothing that can be done to compensate for the fact that 1" farther from the throat may show 0.001" (or more) runout. What can be done to compensate for that is to use two points, one in the throat, one an inch, or more, beyond, to establish the bore segment that is aligned with the spindle axis. Then, when the drilling and boring is done, the third point is created that in fact exactly aligns the chamber with the bore segment that begins at the throat and proceeds an inch or more beyond it which is exactly what Gordy's method was designed to do.

That is the difference between how most do it and Gordy and those that follow his approach do it. That said, I don't know if the difference matters or not. Gordy thinks it does, those who don't use his approach think it doesn't. I rather suspect there is no <light bulb moment> that will cause folks to change their opinion. Some folks will do it one way, some will do it the other.

Rifles done using either approach have shot world records. One approach may increase the odds of a "hummer", or not. I certainly don't have the money or time to set up a statistically significant experiment which would require doing about 32 barrels with each approach (64 total) and then having the shootout using a rail gun in the Houston Wearhouse (which is sadly no more) to take pretty much all the human element out of it as the definitive test. That's not going to happen. But if it did, and we got a difinitive answer, there would be the next topic to keep the forum discussions going.

May your reamers not chatter, your actions be true, and your groups no bigger than caliber sized bullet holes. One can always hope ...

Fitch

 

[Jim Borden]

Ditto

Jackie
You said what I was saying using different words-thanks!

Jim

 

[JerrySharrett]

Jackie
You said what I was saying using different words-thanks!

Jim

Jim Borden and I had a long discussion by phone this morning. What we both are saying is the same thing, so is Jackie. The main requirements of accurate chambering of this "curved" barrel is to have the important points in common along a straignt line. Those points being in common and turning true and concentric with the lathe spindle axis of rotation. These three required points being, the bullets exit point of the muzzle bore, the exact rotational center in the barrel where the bullet engages the rifleing, and the exact rotational center of where the reamer body contacts the bored hole that was bored to remove meat and establish that required third point for reamer guidance.

Both Jim and I feel that the third point mentioned above will give the reamer better guidance if it is a straight bore that allows just a ring of contact than if it is the conical profile of the chamber body. There could possibly be too much bias exhibited if the body's roughed bore were tapered to allow the entire reamer body to be influenced by full contact of that tapered bored hole.

 

[frwillia]

Jim Borden and I had a long discussion by phone this morning. What we both are saying is the same thing, so is Jackie. The main requirements of accurate chambering of this "curved" barrel is to have the important points in common along a straignt line. Those points being in common and turning true and concentric with the lathe spindle axis of rotation. These three required points being, the bullets exit point of the muzzle bore, the exact rotational center in the barrel where the bullet engages the rifleing, and the exact rotational center of where the reamer body contacts the bored hole that was bored to remove meat and establish that required third point for reamer guidance.

Both Jim and I feel that the third point mentioned above will give the reamer better guidance if it is a straight bore that allows just a ring of contact than if it is the conical profile of the chamber body. There could possibly be too much bias exhibited if the body's roughed bore were tapered to allow the entire reamer body to be influenced by full contact of that tapered bored hole.

I've not done the pre-boring yet, but I agree with you folks that it's a heck of a good idea regardless of which approach is used for alignment. Having decided to do the boring, I'm trying to figure out the best way to do it. That leads to 2 questions:

1. Do you bore it so the reamer pilot can be in the bore when the reamer flutes engage the bored hole?
2. How deep do you bore when you have a long skinny cartridge like a .30-06?

Thanks
Fitch

 

[Butch Lambert]

Fitch,
It seems to me that you are saying that using the Gritters method would straighten the bore. That is the way that I interpret what you are saying.
Butch

 

[frwillia]

Fitch,
It seems to me that you are saying that using the Gritters method would straighten the bore. That is the way that I interpret what you are saying.
Butch

Not exactly. The bore is the bore and wanders where it wanders - Gritter's method doesn't do anything about that.

I'm saying two things:

1. Gritters method will place the chamber almost perfectly in line with the bore segment at and just beyond the throat - which is the only part of the bore that's important when chambering.
2. His method results in cutting the crown so the plane of the crown is almost perfectly orthogonal to the axis of the bore at and approaching the muzzle.

It won't straighten the bore in the sense of changing how it wanders around inside the barrel, it just aligns the chamber with the part at the breech end, where ever that happens to be pointing, and results in a crown that should have the best possible symmerty at bullet exit.

If the bore were dead straight, or the bore segment at and just beyond the throat happens, through pure chance, to be aligned with the virtual centerline between the point at the muzzle and the point in the throat, the chamber to bore alignment is the same for both methods.

Fitch

 

[Butch Lambert]

Fitch,
If as has been said before, you indicate the groove at the throat and drill and bore to that point you will have a hole that is straight from the back of the chamber to the throat. You have no control of what the barrel does in front of that point.
Butch

 

[JerrySharrett]

I've not done the pre-boring yet, but I agree with you folks that it's a heck of a good idea regardless of which approach is used for alignment. Having decided to do the boring, I'm trying to figure out the best way to do it. That leads to 2 questions:

1. Do you bore it so the reamer pilot can be in the bore when the reamer flutes engage the bored hole?
2. How deep do you bore when you have a long skinny cartridge like a .30-06?

Thanks
Fitch

Fitch,
1 Yes.

2 Look at the reamer body. Drill a hole that is about 0.020-0.030" smaller in diameter than the cartridge is at the shoulder and stop the drill about 1/8" or so before where the cartridge shoulder will end. Then take a couple of light boring cuts about 0.005"/side and about 3/4" or so deep. What you will find is that the reamer bushing will enage the bore about 1/2"-3/4" before the reamer body starts cutting.

That is why it is best to have a straight hole not a tapered one, IMO. An experienced machinist like Jackie will have his compound set precise enough that in that situation it will not bias the chamber orentation. But if, say a novice, gets the angle wrong or cuts too much he may overbore the chamber.

If you are in doubt of what I am trying to explain, start the process by drilling more shallow, then and boring more shallow than I suggested above. Then insert the reamer and think about what is enagaing and where. I think you will end up in the general area I explained above on just about any bottle-neck cartridge.

 

[JerrySharrett]

Something that may clarify some of my explanation. We all remember from plane geometry that a straight line can be established through two points. A curve can be established by three non-linear points. In the explanation above there are three linear points along that straight line which is along that exact rotational line which is the spindles axis. BUT, that third point that is along the spindle axis is generated when you do the pre-boring operation.

 

[Butch Lambert]

Jerry,
If you indicate the flute on your reamer and move your compound so the indicator shows "0" then your boring bar will bore the exact angle that the reamer cuts.
Butch

 

[Greg Walley]

As to out-of center at the muzzle....the last 2-3 years the OD is out of concentricity with that pin by about 0.007"-0.010". But, realize, the muzzle bore is dialed in with the chamber neck/body/tenon/tenon shoulder.

Remember in dialing in a barrel simultaneously at both ends, the most curve is about half way between.

....When I remove a zeroed barrel I cambered and screw another on, the POI will easily be within 2" at 100 yards....

Thanks for the information Jerry. Apparently this alignment artifact is not an issue for you…you are getting lucky having the bores on your blanks relatively centered at the muzzle end of the blank where you cut it off, and you’re establishing the breech end of the blank on an axis that allows the entire length of the barrel to be perpendicular with the action face.

I’m wondering if the reports of widely varying POI from barrel to barrel that I hear of on occasion are from a combination of improper technique when dialing in the irregular features in the bore; subsequently bending the barrel while cutting the tenon, or if it is caused by the recent method of indexing the bend in the bore at the muzzle. Maybe it’s a combination of both.

I have two different ways of checking a barrel after it has been chambered for straightness in relation to the tenon. My methods won’t win any awards in metrology from the NIST or ISO, but they are a facile way for a gunsmith or home machinist to verify the soundness of their barrel chambering methodology. I’ll try to post some photos and a detailed description of the procedure when I get a chance.

Greg Walley

 

[JerrySharrett]

Thanks for the information Jerry. Apparently this alignment artifact is not an issue for you…you are getting lucky having the bores on your blanks relatively centered at the muzzle end of the blank where you cut it off,

Greg Walley

No Greg. I'm not lucky in that my muzzle bores are running close with the muzzle OD. Remember, I am dialing in the muzzle BORE using a gage pin. The muzzle OD sometimes runs out so much that when I turn the barrel around and crown it, the burr created on the OD has to be removed with a file. If I cut it off with a tool the end would look goofy as the OD's bevel would be way off.

On lathes that have long headstocks and depend on using a bushing on the muzzle OD, ID to OD runout would be a problem. By hey, just index it!!