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Old 09-05-2018, 04:31 PM   #1
kck
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Default Chucking a Proof barrel

Going to chamber a Proof CF barrel for the first time and was wondering if anyone had anything they might do different as far as chucking it. It obviously has plenty of room on the shank end to hold with the standard aluminum shims but as far as holding for threading and crowning the muzzle is where I'm a bit concerned. I know that CF is pretty dang tough so thinking brass shims would be OK to not bugger it up as long as it's not too terribly tight? Any help would be greatly appreciated!
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Old 09-05-2018, 05:08 PM   #2
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go directly to the source … call PROOF and ask their GS's opinion and recommendations
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Old 09-05-2018, 05:42 PM   #3
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Going to do that as well but I always like to ask around in case the seasoned guys have some different little tips or tricks. Updates to come and I'll try to do a video based on what I find out.
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Old 09-05-2018, 05:47 PM   #4
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go directly to the source call PROOF and ask their GS's opinion and recommendations
THIS... or call Stick1 and see if what he has exsperienced
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Old 09-05-2018, 06:04 PM   #5
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I'm certainly not "seasoned", working on my first barrel job now, and waiting for ATF to call me about the FFL. Here's my thought, tell me what you think:

I built a jig for truing actions based on Mike Bryant's design. It's basically a piece of steel tubing about 3" long with a 1.75" ID and thick walls with eight 1/2"-20 cap screws for adjustment..... basically two spiders on one short section of tubing. I then made an aluminum collet of sorts that fit inside that fixture with about 25-30 thou clearance, and an ID that fit the front action ring close, cut four slots about 3/4 of the way down the collet so it'll clamp on the action. Now I can load the action into the collet and the collet into the fixture and align it to run true using the 8 jacking bolts without bending or stressing the action.

Now, back to your question, what's stopping me from cutting a collet to fit the barrel and holding it the same way? I can promise you that setting the action up in that fixture to run dead true was WAY FASTER than setting up my barrel by holding the chamber end in the 4 jaw chuck and rne muzzle in the outboard spider...... not to mention I'm pretty sure the barrel is under stress between the chuck and spider. I know the muzzle is way farther off center than it should be. I'm going to remove it from the lathe and turn a collet to fit the barrel and try it again that way.

Below is a picture of my fixture and collet.

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Old 09-05-2018, 09:44 PM   #6
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Originally Posted by kck View Post
Going to chamber a Proof CF barrel for the first time and was wondering if anyone had anything they might do different as far as chucking it. It obviously has plenty of room on the shank end to hold with the standard aluminum shims but as far as holding for threading and crowning the muzzle is where I'm a bit concerned. I know that CF is pretty dang tough so thinking brass shims would be OK to not bugger it up as long as it's not too terribly tight? Any help would be greatly appreciated!
That carbon fiber is indeed tough.......but it will compress as it sits under stress. Meaning that your perfectly indicated bore likely won't be perfectly indicated if you come back and check it 30 minutes later. This will kind of address TxFireguys issue as well concerning his steel barrel indicating.

First, we know that not many bores will run true to the outside dimensions of the barrel once you get very far from either end. They will generally have some degree of hook or cork screw that can cause a problem when indicating on the bore itself, but holding the barrel in the chuck's perfectly flat jaws locked against the barrel's perfectly flat outer surface. If the bore was dead straight there would be no issue holding it in the outboard spider and directly in the chuck jaws, but they aren't dead straight. By setting up like this, you are basically bending the barrel to conform as you are indicating it. Not a good idea. The barrel needs to be able to pivot at 1 end to keep from bending, but still be held securely enough to be able to dial in and perform the work that needs to be done. There are several ways to accomplish this. The old tried and true (and most economical) way to do this is by holding the barrel in your chuck jaws with some sort of ring around the barrel.

Number 4 copper ground wire works really well for this. Preferably really weathered wire that came off an old power pole The stuff is hard as woodpecker lips and will take a lot more pressure than any of the newer copper wire you can find today. You'll likely need a small hammer to form it around the barrel if it's the good stuff. I have a pile of rings for just about every size barrel sitting on my bench from when we chambered on the manual lathes. One for the breach end, and another smaller one for the muzzle end when the barrel is swapped around to work on crowns/muzzle threads. We use simple 1/8" thick aluminum pads on the outboard spider side.

The issue with using the ring on the muzzle end of a carbon fiber barrel goes back to material compression. We made a series of 1.5" long aluminum "sleeves" with an internal taper to match all of the Proof and Hardy barrel profiles and a ring to fit over the sleeves. The sleeve distributes the stress of the ring over a larger area and allows it to be held very securely without compromising the barrel. Simple but effective. There are a million ways to skin this cat, but maybe this will give you some ideas to work with.

-Robert
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Old 09-05-2018, 10:10 PM   #7
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That carbon fiber is indeed tough.......but it will compress as it sits under stress. Meaning that your perfectly indicated bore likely won't be perfectly indicated if you come back and check it 30 minutes later. This will kind of address TxFireguys issue as well concerning his steel barrel indicating.

First, we know that not many bores will run true to the outside dimensions of the barrel once you get very far from either end. They will generally have some degree of hook or cork screw that can cause a problem when indicating on the bore itself, but holding the barrel in the chuck's perfectly flat jaws locked against the barrel's perfectly flat outer surface. If the bore was dead straight there would be no issue holding it in the outboard spider and directly in the chuck jaws, but they aren't dead straight. By setting up like this, you are basically bending the barrel to conform as you are indicating it. Not a good idea. The barrel needs to be able to pivot at 1 end to keep from bending, but still be held securely enough to be able to dial in and perform the work that needs to be done. There are several ways to accomplish this. The old tried and true (and most economical) way to do this is by holding the barrel in your chuck jaws with some sort of ring around the barrel.

Number 4 copper ground wire works really well for this. Preferably really weathered wire that came off an old power pole The stuff is hard as woodpecker lips and will take a lot more pressure than any of the newer copper wire you can find today. You'll likely need a small hammer to form it around the barrel if it's the good stuff. I have a pile of rings for just about every size barrel sitting on my bench from when we chambered on the manual lathes. One for the breach end, and another smaller one for the muzzle end when the barrel is swapped around to work on crowns/muzzle threads. We use simple 1/8" thick aluminum pads on the outboard spider side.

The issue with using the ring on the muzzle end of a carbon fiber barrel goes back to material compression. We made a series of 1.5" long aluminum "sleeves" with an internal taper to match all of the Proof and Hardy barrel profiles and a ring to fit over the sleeves. The sleeve distributes the stress of the ring over a larger area and allows it to be held very securely without compromising the barrel. Simple but effective. There are a million ways to skin this cat, but maybe this will give you some ideas to work with.

-Robert
Yessir, I used the copper wire ring method around my barrel, and felt like it pivoted on the wire fairly well, adjustments seemed to be predictable etc. Then, I went to determine which side of the bore was "pointing up" so I could clock the barrel on the action with it pointing to 12 o'clock. That's when I noticed how far off center it was..... enough that my Inrerapid indicator won't read it, even on the outside of the barrel..... it's easily visible runout. I'm going to try my collet idea and see how it works, otherwise it's back ti the drawing board. The wire I used was actually 1/4" copper rod (round) and seemed hard, very hard to bend, but maybe it's soft enough that it's gripping the barrel still and causing the heavy sporter barrel to flex some. I may also try just releasing the tension on the spider and see if it changes my runout on the chamber end. If not, I'll just snug it back up without bending the barrel, but i'm afraid as soon as I let the tension off, it's going to move all around.

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Old 09-06-2018, 12:22 AM   #8
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Yessir, I used the copper wire ring method around my barrel, and felt like it pivoted on the wire fairly well, adjustments seemed to be predictable etc. Then, I went to determine which side of the bore was "pointing up" so I could clock the barrel on the action with it pointing to 12 o'clock. That's when I noticed how far off center it was..... enough that my Inrerapid indicator won't read it, even on the outside of the barrel..... it's easily visible runout. I'm going to try my collet idea and see how it works, otherwise it's back ti the drawing board. The wire I used was actually 1/4" copper rod (round) and seemed hard, very hard to bend, but maybe it's soft enough that it's gripping the barrel still and causing the heavy sporter barrel to flex some. I may also try just releasing the tension on the spider and see if it changes my runout on the chamber end. If not, I'll just snug it back up without bending the barrel, but i'm afraid as soon as I let the tension off, it's going to move all around.

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"Then, I went to determine which side of the bore was "pointing up" so I could clock the barrel on the action with it pointing to 12 o'clock. That's when I noticed how far off center it was..... enough that my Inrerapid indicator won't read it, even on the outside of the barrel..... it's easily visible runout."

If you are trying to use the "clock the barrel" approach, you are almost always going to see that kind of runout by default. Since the method hinges on indicating over an entire section of the bore instead of a single point in the bore running parallel with your set up. Basically you have a straight barrel with crooked bore in most cases, so anything you do to get the crooked bore running "straight" will just manifest itself as runout on the outside of the barrel. Most guys using this approach will ignore what the other end of the barrel is doing at this point as it will be dealt with in the same manner when it's flipped to work the other end. They will simply mark the "high spot" and do the clocking as a separate step at the end of the process, after the barrel has been test fitted to the receiver under actual torque values to determine where the high spot will land. I get the theory to the method - the bullet enters a "straight" section of the bore and leaves a "straight" section of the bore. I have used it with good results many times, but I'll never do one like that again. I find it an overly complicated method that has several potential pitfalls, and provides no advantage over a couple of other methods that produce much more consistent results. With any method using an outboard spider, you will need that pivot point to minimize bending forces being applied to the barrel to some degree.
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Old 09-06-2018, 01:26 AM   #9
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"Then, I went to determine which side of the bore was "pointing up" so I could clock the barrel on the action with it pointing to 12 o'clock. That's when I noticed how far off center it was..... enough that my Inrerapid indicator won't read it, even on the outside of the barrel..... it's easily visible runout."

If you are trying to use the "clock the barrel" approach, you are almost always going to see that kind of runout by default. Since the method hinges on indicating over an entire section of the bore instead of a single point in the bore running parallel with your set up. Basically you have a straight barrel with crooked bore in most cases, so anything you do to get the crooked bore running "straight" will just manifest itself as runout on the outside of the barrel. Most guys using this approach will ignore what the other end of the barrel is doing at this point as it will be dealt with in the same manner when it's flipped to work the other end. They will simply mark the "high spot" and do the clocking as a separate step at the end of the process, after the barrel has been test fitted to the receiver under actual torque values to determine where the high spot will land. I get the theory to the method - the bullet enters a "straight" section of the bore and leaves a "straight" section of the bore. I have used it with good results many times, but I'll never do one like that again. I find it an overly complicated method that has several potential pitfalls, and provides no advantage over a couple of other methods that produce much more consistent results. With any method using an outboard spider, you will need that pivot point to minimize bending forces being applied to the barrel to some degree.
Sorry to have hijacked your thread OP.

So, basically, I got my chamber end running true by measuring runout with the long contact indicator as far in as it would reach, and right at the edge of the bore. I adjusted the 4 jaw chuck, clamping against a copper ring running around the barrel shank, af well as the outboard spider bolts on the muzzle, until the chamber was running true. Measuring on top of the lands, I'm running as true as my eye can see on the Interapid .0005" indicator, over a span of 2.75". Checked numerous places in between. I then cut off about 1/2" of barrel to make the taper fit my stock channel a bit better, threaded and cut a counter bore, then measured runout again with no change (except now i can reach further into the barrel) still no runout that I can measure. During all that, I completely ignored the muzzle end after I got the chamber end running true.

My plan was to figure out how the barrel needed to be indexed, although I don't know why, since I'm going to cut 4-5" off when done, the bore might not be pointing the same way in that section as it is at the end of the full length blank. My thinking though, is that I needed to do it now, since the only way I know to clock the barrel is by removing material from the barrel shoulder, so that needs to be done before chambering. The more I think about it though, how do the guys that run prefits clock their barrels? They don't worry about it, they set headspace and lock down the barrel nut. I may take that approach and go ahead and chamber with the current setup, then flip it around and indicate on the muzzle end and cut it off, cut my crown and go shoot.

I still want to try my collet idea, but I'll do it on a take off barrel first. My basic idea is that it keeps all the stresses and what not over a shorter, thicker and stiffer section of barrel, reducing the chances of bending to nearly zero. I'm fairlycertain I'm seeing bending now, even with the wire pivot ring. I'd love to buy one of the Truebore Alignment chucks, but I think I'd be better served by spending my money on practice stock at this point. That dude is proud of that chuck...... my collet idea sort of acts the same way though, you clamp onto a section of barrel maybe 2-3 inches long, then adjust the clamp around until you're running true, and let the other end "float" out there wherever it needs to be so the chamber section is running true when the reamer goes in. Basically, it would take the pivot ring out of the equation and replace it with a 3" long sleeve cut to fit the barrel taper. Then, since I'm using 1/2" bolts on both ends of that sleeve, I can pivot the whole assembly around as needed. Am I way off base, or even making sense?

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Old 09-06-2018, 02:33 AM   #10
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That probably explains why you were seeing so much runout if you were trying to measure the bore from the throat area all the way back to the end of the barrel and get it all running true. Everything from the throat back doesn't really matter. What does matter is where your bullet will actually make contact with the bore. Indicate on that point. Your chamber will clean everything up from there back, and it will all be running concentric to your bore where the bullet actually sits. I would also recommend taking your readings off the grooves rather than the lands, especially on 5R barrels.
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Old 09-06-2018, 07:50 AM   #11
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That probably explains why you were seeing so much runout if you were trying to measure the bore from the throat area all the way back to the end of the barrel and get it all running true. Everything from the throat back doesn't really matter. What does matter is where your bullet will actually make contact with the bore. Indicate on that point. Your chamber will clean everything up from there back, and it will all be running concentric to your bore where the bullet actually sits. I would also recommend taking your readings off the grooves rather than the lands, especially on 5R barrels.
Okay, I see how measuring where the throat will end up will make the chamber concentric at that point, but it won't be aligned axially necessarily. Are you then going to the muzzle end and aligning it there, or just getting it concentric at the one spot? I feel like measuring at the two points gives the same axial alignment that running a bushing on a tapered indicating rod into the bore and measuring runout on the rod in two spots would.

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Old 09-06-2018, 09:49 AM   #12
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The issue with using the ring on the muzzle end of a carbon fiber barrel goes back to material compression. We made a series of 1.5" long aluminum "sleeves" with an internal taper to match all of the Proof and Hardy barrel profiles and a ring to fit over the sleeves. The sleeve distributes the stress of the ring over a larger area and allows it to be held very securely without compromising the barrel. Simple but effective. There are a million ways to skin this cat, but maybe this will give you some ideas to work with.


Gotcha. Yessir, this is kinda what I was looking for as I also felt that it would be best to distribute the pressure over a greater area when trying to hold the muzzle end. Great input and much appreciated. May make an aluminum slotted sleeve with internal taper to match the contour of the muzzle similar (I think) to what you did. I'll try to update as I go as well.

Last edited by kck; 09-06-2018 at 09:55 AM.
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Old 09-06-2018, 10:14 AM   #13
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Not a gun smith but machine engine parts we have to hold +/- .0001 on avg over a large bore and it has to straight and round once final hone..

So with that in mind am I reading this right.. Check OD with TIR of barrel and you find that the bore is not centered ?? ?? I mean we see it all the time , but for us its not a factor cylinder can move some and piston can slide on wrist pin .
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Old 09-06-2018, 10:25 AM   #14
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Not a gun smith but machine engine parts we have to hold +/- .0001 on avg over a large bore and it has to straight and round once final hone..

So with that in mind am I reading this right.. Check OD with TIR of barrel and you find that the bore is not centered ?? ?? I mean we see it all the time , but for us its not a factor cylinder can move some and piston can slide on wrist pin .
That's correct, sort of. The barrel bore isn't necessarily centered, and never dead straight. It may be centered in one spot on one end, then 1/2 way down the tube, it may be several thousandths off center. The issue is not in placing the hole to start, it's that it's impossible to drill a perfectly straight hole that's 50-60 times the diameter. The bit wanders, but you know that. So for that reason, gunsmith's indicate to the ID, not the OD. There's are several methods of taking that measurement, and that's what Stick1and i are discussing. I've seen where some guys get it running concentric at the chamber end and the muzzle end and ignore what's in the middle. I've seen some that use an indicating rod riding on the bore and hanging out the chamber end and the measure tir on the rod. I've also seen a method that uses a bushing on a rod ands ther rod is held in the trailstock. The bushing is run into the bore a certain distance and the TIR is measured right where the rod enters the bore, then it's repeated in several spots throughout the chamber area of the barrel..... this one makes the least sense to me, but I understand it gets good results for those who use it.

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Old 09-07-2018, 05:59 PM   #15
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Heard back from DJ at Proof a bit ago. He said that brass shims in a 4 jaw should be just fine as long as I don't crank the hell out of if. Should be able to update through the next week.
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Old 09-08-2018, 03:22 PM   #16
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That's correct, sort of. The barrel bore isn't necessarily centered, and never dead straight. It may be centered in one spot on one end, then 1/2 way down the tube, it may be several thousandths off center. The issue is not in placing the hole to start, it's that it's impossible to drill a perfectly straight hole that's 50-60 times the diameter. The bit wanders, but you know that. So for that reason, gunsmith's indicate to the ID, not the OD. There's are several methods of taking that measurement, and that's what Stick1and i are discussing. I've seen where some guys get it running concentric at the chamber end and the muzzle end and ignore what's in the middle. I've seen some that use an indicating rod riding on the bore and hanging out the chamber end and the measure tir on the rod. I've also seen a method that uses a bushing on a rod ands ther rod is held in the trailstock. The bushing is run into the bore a certain distance and the TIR is measured right where the rod enters the bore, then it's repeated in several spots throughout the chamber area of the barrel..... this one makes the least sense to me, but I understand it gets good results for those who use it.

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So in my world we have to bore and hone the cylinder so to hold +/- 2 tenths you must work with what you have which is never concentric to OD of cylinder in fact its 3-5 thou out . So for use it must be round and straight so it can get dicy some times as we have to load the cylinder with tq plates to establish normal distortion .

Now I can see where a barrel would distort as well from the ignition to heat to the bullet being engaged into the rifling . Barrel thickness I am sure all works into this ..

Again I do not work on them I reload or at least to any longer I just buy them done ha ha no time


So when you do this are you using a 3 jaw or a 4 jaw I would think you are running a 4 jaw due as you have more options with that



Can it be EDM perfectly straight ?? My only dealings are small holes in thick injection molds
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Old 09-08-2018, 04:06 PM   #17
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That's above my pay grade, but that EDM comment ...... I know nothing about edm other than the fact that it's incredibly accurate. Surely some barrel maker had experimented with it..... is there a maximum distance you can reach with edm? That might actually be the next greatest method in barrel making, but again, beyond my pay grade.

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Old 09-08-2018, 08:51 PM   #18
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Okay, I see how measuring where the throat will end up will make the chamber concentric at that point, but it won't be aligned axially necessarily. Are you then going to the muzzle end and aligning it there, or just getting it concentric at the one spot? I feel like measuring at the two points gives the same axial alignment that running a bushing on a tapered indicating rod into the bore and measuring runout on the rod in two spots would.

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This is a great discussion and illustrates that there are many ways and methods to get the job done. It's interesting and sometimes frustrating coming up with a system that works for you and provides consistent results. My thoughts are as follows.

The issue with the tapered rod is that it is centering on a portion of the bore behind the bullet that will no longer be there when you cut your chamber, and the bullet does not care or is not influenced by whats behind it. It is influenced by how straight it enters the bore and what it encounters in front of it. Additionally, I and every other builder I have discussed this with have observed that the tapered rod measurements are not repeatable. Dial in and take a reading, then pull the rod and rotate it 180 degrees and take another reading. You'll see runout that wasn't there before almost every time. The micro burrs from taking a simple facing cut will alter the results. Take a .001 facing cut and try it again

We know that there is no such thing as a perfectly straight bore, so we deal with it the best we can. The longer section of crooked bore you try to manipulate into a straight line with your set up, the more you are throwing the outside of the barrel and your muzzle off the center-line or axis. Someone who has built more record holding rifles than about anyone in the industry told me when discussing this issue once that "you can't control the path of the bore, but you CAN control where your bullet enters and exits it".

I found kind of a light bulb moment in that statement. If you think of the bullet and it's relationship to the bore as a train and a track, or a roller-coaster and it's track, you'll get the picture. The bullet(train) is going where the bore(track) takes it. You can't change it or straighten out the curves, as the track is already laid. It's going to zig and zag on it's journey down the track, but if it starts and leaves on the same plane, you know EXACTLY where its going to go and it doesn't really matter what it does in the middle. When you start trying to make the curve straight and inducing large amounts of external runout on one end, then try bringing it all back together by "clocking" the runout in your favor on the other end, you are losing control of keeping everything within the axis of the system.

All that said, if you were to dial in on the exact spot your bullet was to make contact with the lands, and at the same time dial in your crown on the outboard spider, would you not know exactly where the bullet was going to enter and exit the bore? Would both points not be dead true to the center line of the entire system? If you used a ring on the inboard side as a pivot point to keep from binding or bending the barrel, would you not get repeatable results that would produce barrel after barrel that shoot to the same exact P.O.A? Yes you would

A few top benchrest smiths have been using this technique successfully for many years. It produces fantastic results and guys can swap barrels, make a minor scope adjustment and continue on with minimal adjustments as it is that consistent. Mostly due to keeping control of the variables that CAN be controlled and keeping the most important points in-line with the center of the system. I can and have re-barreled rigs for guys who will call me back later and say that the new barrel was hitting within 1 MOA of the old one right out of the gate using this method.

As far as axial alignment, how much do you really need? I'd argue that you don't need .001 more than the length of the bearing surface of the bullet itself, and only in that portion directly in front of where it first contacts the lands. After that short distance the bullet is fully captured by, and is riding the lands(tracks) so you have no more influence over it anyway. Your pre-bore will control everything from that point back. So it started straight - mission accomplished! I promise it is much easier to align a .150" section of crooked bore straight than it is to try doing it with 3". And you won't be contorting your muzzle end until it's pointing at the ceiling and having to go back and "clock"the muzzle to try to straighten things back out. And as a bonus, your barrel will actually be pointing straight, and it will even run straight down the barrel channel as it was meant to

In the end, none of these curves or hooks are extreme. They are easy enough to work around in most cases with a good dial indicator and some common sense....... and without giving up control of where the bullet goes when it exits the muzzle. Then again, Chad Dixon has said on more than one occasion that a guy could set up a barrel between centers and take a skim cut to true up the cylinder portion, then chuck it up in a 3-jaw and punch it with a floating reamer holder, never once indicating anything and end up with a better than good chance of a good shooting barrel. So maybe we are all overthinking this

-Robert
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Old 09-08-2018, 09:32 PM   #19
txfireguy2003
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That all makes great sense, and I agree we are probably overthinking it a bit, but i think that's in our nature, just like welders tend to overbuild everything, gun guys tend to go to ritualistic lengths to get the absolute best accuracy..... it's what we do. Hell, i've got a crooked factory Remington 308 that groups Hornady ammo into one ragged hole and God knows they didn't go to any special lengths to build that one.

I guess my confusion is with the idea of starting straight when your chamber is not aligned with the bore, but again, either method is about guaranteed to give you a straighter entry than your average factory rifle, add to that a trued action, quality barrel, sharp reamer..... you'd probably have a hard time NOT building an accurate rifle when you consider that most manufacturers are producing sub moa rifles by throwing them together with sub par parts. I'm going to finish this barrel indicated as I have it since i've already started with this setup. I will probably use your method on the next and see which i like better. I do like the idea of not having to clock the barrel for sure.

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Old 09-08-2018, 10:51 PM   #20
Stick1
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"I guess my confusion is with the idea of starting straight when your chamber is not aligned with the bore,"

It is very much aligned with the bore if you think about it. The bore is wandering all over the place from end to end if only by a few thou, though often much more. Given that bore location is not a constant throughout the length of the barrel, the best you can really do is pick a point or section of bore to indicate on no matter which method you use. The question is, which section? Picking the spot where the bullet actually enters the bore would obviously be the most important area to get running true. If you use a SAAMI 6.5 CM as an example, that area would be about 2.208" in the bore. Indicate on that spot using DIRECT contact with your DTI and dial in. Now you are running true on that section based on real/repeatable measurements. Cut your tennon and threads to spec. Now drill/pre-bore/punch your chamber...done. ALL of these operations are now PERFECTLY aligned to your bore, unless something shifted or you moved your set-up. It has no choice but to be aligned. If you did it right, the pre-bore kept your reamer from wandering and you ended up within .0001 of dead straight with the spot you indicated on before you started cutting.

You can easily see why you can't get that precise using range rods. First,you cant measure exactly where your throat is going to be, so how can you cut your chamber concentric with the bore in that spot? Second, you already know the bore between the throat and the back of the chamber is probably curved, so no good/accurate measurement will be obtainable by sticking a straight measuring tool into a curved bore. Especially one that "self centers" on an area far away from the part you are trying to measure. It could only work if the bore WERE straight. The piloted end has is own set of issues as well, since a pilot has to have clearance(read error) to fit in the bore, and more clearance (more error) to fit on the tool in the first place. Consider all of the known error in that system then double down by taking readings way outside the actual bore where the deflection and error is multiplied every inch that thing is sticking out of the barrel. If your goal is to cut chambers concentric to the bore, these things can lead you in the opposite direction real quick. I only say this because I have tried it. I have every size up to .375 that turned out to be a really expensive failed experiment. They are good for a few other things though like roughing in, checking pilot fit and clearances on muzzle devices.
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Old 09-08-2018, 11:38 PM   #21
txfireguy2003
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Yeah, i understand all that about the rods for sure. What I don't understand is the alignment thing. I'm going to try and explain my confusion, but might fail, so i apologize in advance. Let's assume a full straight barrel, 1.25" from chamber to muzzle, and let's assume the bore is actually centered on both ends, but we know it's curved in between the two ends by some amount. So I reach inside to the point where my bullet is going to contact the rifling, and adjust the chuck until i've got zero runout there. I see that bore looking like a jump rope as it spins around my indicated point, and the muzzle which was also set to zero tir during initial setup. So say the bore makes a 2 degree angle as it diverges from the original center line of our barrel (i know that's way exaggerated, but it illustrates the point). So i indicate the throat and get it running true, isn't the bore still leaving my center line at an angle? Wouldn't the bullet leave the chamber and immediately make a sharp 2 degree turn in order to mount up on those railroad tracks? We're already concentric because we indicated there, so we're between the rails, but a straight line will cause us to hit one rail, turn, catch the other rail then align ourselves and ride the rest of the way down. We're starting out trip with a sudden turn.

Please don't think i'm arguing, you're clearly the expert here, i'm trying to learn, but i've got to actually see it in my head. The way i was doing it, i follow the original bore, at that 2 degree angle, so the bullet starts into those train tracks smooth and straight to begin with, no 2 degree sideways jolt getting onto them. Agreed, once he's on the tracks, he's gotta go where they go.

What about your crowns? Do you cut them square and concentric to the bore, or square to the overall centerline of the system? If our theoretical bore returns to center at a 2 degree angle, do we cut the crown square to that angle?

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Old 09-09-2018, 01:22 AM   #22
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Fireguy, if I missed anything that's been discussed in the prior posts (other than how to chuck on a CF barrel ) just tell me I'm an idiot...my wife does all the time...hahaha. The following is my humble *** opinion and I could be wrong. Anyway, we know the bore of a barrel isn't perfectly straight, we've identified that. The best we can do is give our projectile as perfect of a path to start and finish, what happens between those points is a bit out of our control. Indicate and cut your crown concentric with the bore and that will make it square (I see what you're saying about the angle) and yes, you do cut it with the line of the bore, or a small section of it, from indicating that length. I feel that this is where you'll then align your scope to the path of the projectile, find a load that allows for consistent barrel whip, allowing your bore to return to a consistent spot as the bullet leaves the bore/crown. Speaking of crown, I've had my last one

Last edited by kck; 09-09-2018 at 01:32 AM.
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Old 09-09-2018, 11:26 AM   #23
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txfireguy2003 - Don't think you're arguing at all, brother. KCK - hope you got your barrel chucked Sorry for the hijack.

Fireguy - I'm probably not doing a good job of explaining it clearly, which I'm pretty well known for The problem with trying to address the 2 degree divergence example above is that it has a path of straight departure away from the reference point, it is linear but we are actually dealing with an arc that is constantly changing over distance like a corkscrew. However we describe it, its going to be there no matter what we do and the bullet is going to follow it no matter how concentric or out of whack the chamber is. We can't move it or relocate it, so we agree we are stuck dealing with it.

I think what we are trying to address is how we can cut a chamber and start a bullet straight with a bore that is not straight. I go a post or two back where I asked how much of the bore needed to be running "straight" in order to start the bullet straight. I think that "start" is the key here. Once it engraves its entire bearing surface, its "started" and the bore owns it from that point forward. So you are looking at a very short area that needs to be running true to accomplish this(which is good when you're trying to make a corkscrew "straight"). Unless you are talking about a really sharp turn(which is not going to happen as we're talking about very minor drift in a bore over a short distance) there is nothing for the bullet to slam into, and it is fully captured and supported anyway. Hopefully that makes sense. When you flip it around to work the muzzle end you would then dial in on the crown and the chamber that is now in the outboard spider. At that point, your chamber and throat will be running on the same plane as your bore at the muzzle. Now you control where the bullet exits in relation to the center line of the entire rifle.
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Old 09-09-2018, 12:09 PM   #24
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Haha all good. Glad you're in on this one Stick, tons of great info for me as well
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Old 09-09-2018, 12:34 PM   #25
txfireguy2003
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That makes sense.

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