This may be a silly little question, or opening a can of worms. But, we talk much about keeping a barrel straight, slugging bores and chambers to gain understanding of dimensions, alignments of chambers to bore, and some notion of bore size down the barrel.
Working between centers addresses issues of aligning the two ends of the bore...
But, what of the straightness of the bore between those two points?
With the improvements in modern machining deep hole drilling has gotten much better and effient. The advent of the hollow drill and thru coolants at high pressures has made chip clearing much better, the peck drilling cycle on computer controlled machines makes smaller chips that are easier to flush and clear. The computer controlled cutter grinders make for much more accurate drills.
Heat build up can cause things to move around and warp from stresses. Chip build up in the drills flutes can "push" a drill off center. The thru coolant at high pressures will tend to stabilize and stiffen long drills but it has to be maintained. A uneven drill point different angles side to side, off center point or one edge sharper ( wheel loaded ) will walk easily also. Last is a machine with the tail stock off center this can cause the drill to walk. Wear on the side webs also will cause drills to walk.
Looking thru a barrel or deep hole at a bright light the cross in a window frame helps here, if the hole appears oval its not straight thru the blank. A few thousandths can be seen like this.
It seems, from the discussion, that the problem (of straightness) is caused by problems inherent to deep drilling. Hammer forged barrels are not drilled are they? Do they have a straightness problem? (I use the word “problem “ advisedly here, obviously many crooked barrels shoot straight.)
NRA Lifetime member since 1956, NRA Endowment Member. Reloading since 1954. CBA Member Navy Vietnam Veteran USS Intrepid CVA 11
Yes they do. My friend cut his old 110 Savage 22-250 from 24" to 20". the hole in the muzzle was noticably eccentric but it shot better than before.
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Hammer forged barrels start out as a shorter larger dia blank with a hole drilled thru it then installed on a mandrels and as the blank is hammered it gets smaller in dia and longer the hole is formed down to the mandrel which is a mirror of the bore groove and rifling form. When done the mandrel is pressed out. Hammer forged barrels can have a lot of stress in them from the process also. Probably the best for straight holes is the edm process where the electrode never touches the material just the dielectric fluid and the electric arc.
Who does it that way? The edm process.
NRA Lifetime member since 1956, NRA Endowment Member. Reloading since 1954. CBA Member Navy Vietnam Veteran USS Intrepid CVA 11
I believe some pistol makers are now using edm to rifle pistol barrels. In industry a lot is done with edm since the part cn be hardened and the holes or cavities cut after saving warp and finishing work. With the EDM process over burn is figured and an undersized electrode made ( or the undersized electrode is made a given amount under sized .010-.015 usually) and the program writes to this. Electrodes can be carbon, copper copper tungsten mix or for finishing carbide. The electric arc does the work only things that touch the part are the dielectric fluid and the electric arc. Usually 2 electrodes are made a rough and a finisher as they do wear from the electric arc. I did a lot of odd shaped cavities, Holes, threads and other things in our charmalle edm. I have threaded carbide with out an insert. square, rectangular holes, keyed holes pockets for forms and moulds. Our machine could be programed for spirals at distance per revolution or thread pitch so it was capable of doing rifling within it travel limits. A lot of the thread done was a under sized electrode ( under pitch dia) then a flat pocket circle to burn the threads in. I could burn the threads in 60 rc part in 4-5 mins after set up, Carbide took a little longer. A pre drilled and reamed barrel blank with electrode ,020-,025 undersized pushing dielectric fluid thru the blank and electrode would go pretty quick burning the rifling in.
Shine a flashlight on the bolt face and look down the bore. If the bore looks like a consistent spiral the bore is straight enough. The human eye is an amazing quality check device. If the bore is the slightest bit off the spiral of the rifling will not look equal on all sides.
Hick: Iron sights!
I know some premium barrel makers that are very proud of how excellent their straight deep hole drilling capabilities are. I also have seen some not so straight barrels shoot very well.
Stress relieved proper alloy steel is a Huge part of making a great barrel that will shoot well for a very long time, cheap out on the material and it will not last and likely not be repeatable. Then they need to make the rifling consistent. I had one factory barrel that felt like a roller coaster when cleaning it and shot like it was being fired from a moving roller coaster too.
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This has been fodder for much discussion in the past but as someone else said there are no truly straight bores and as others have pointed out it simply doesn't matter. The problem arises when folks machine barrels, chambers and crowns, and set them up as if the bore was straight when in reality it's not! Crowning probably suffers the worst for this when folks go to all the trouble to try and align the muzzle and the breech end by dialing in center for both ends as closely as possible while setting up in the lathe. Due to the normal tolerances for straightness of the bore this will almost always result in a crown that is not perfectly square with the bore, exactly the opposite of what was trying to be achieved.
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Quality & some factory rifle builders often visually check a barrel's straightness. looking at a known straight line through the bore while rotating the barrel to determine if & where it may be bent.
If a bend is observed, they straighten the barrel with an overhead press-cum-barrel-straightening-machine..
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Now I lay me down to sleep
A gun beside me is what I keep
If I awake, and you're inside
The coroner's van is your next ride
Originally Posted by B R Shooter
It's simple, by centering both ENDS of the barrel you are aligning the ends with the spinning AXIS and NOT the bore! The ends themselves may be centered but the less than perfect bore is wobbling around the spin axis. That's why some folks use the much more accurate method of indicating along the length of the long indicator rod, if that rod does not indicate center along it's length then the crown can't possibly be cut true square with the bore! Think about it, how could it? That long snug fitting rod extending from the bore is a true representation of the bore itself (actually an extension of the true location of the bore in relation to that dialed in spinning axis) and if that pin will indicate center only at the muzzle or only at any other single point along it's length then it will wobble when spun. Being an actual representation of the bore then by simple logic if it is wobbling then the bore must be also.
At first I too used the both ends centering method because I was told that's the way it's done but still I wondered why I was finding the indicator would indicate off-center if, after centering at the muzzle, I then moved my indicator farther out? I kept asking myself why when I was told to indicate both ends when setting up was I told to get the indicator reading as close to the muzzle as possible? That didn't make sense because if the rod indicated center at the muzzle but had run-out that got progressively worse as I moved it farther away then the rod is obviously wobbling and if it's wobbling then the bore MUST be also! I started asking questions and found that there has been much disagreement about this and some folks will never accept not centering both ends but it became crystal clear to me when the gun smith I asked about it explained it like this,
Think of an archers bow with the bow itself representing the barrel with the less than perfect bore (a grossly exaggerated example but the principle would be exactly the same). If the ends of this bow were then indicated center in a lathe and spun the string would then represent the spinning axis and that spinning AXIS is what the crown would then be cut to, NOT the bore! He then went on to ask just WHY is it important to center the opposite end from the one being cut? Why would that end of the bore be any more important than any other point along it's length? He then pointed out that of the hundreds of barrels he has done over the last 30+ years not a single one of them would indicate center at the outboard end when the indicator rod was properly aligned so that it would indicate along it's entire length!
The bottom line is that centering the outboard end does absolutely nothing except cause the less than perfect bore to wobble around the axis and will be all but a guarantee that the bore will not be square with the axis at the muzzle which is the only place it matters. By ignoring the outboard center and simply allowing it to go wherever it needs to go in order to align the muzzle indicator rod, and thus by extension the bore at that point, so that the rod will indicate center along it's length then and only then can we cut the crown truly square to the bore at the muzzle.
Statistics show that criminals commit fewer crimes after they have been shot
The problem with that is that while it may be centered with the bore at the indicated point it is not in ALIGNMENT with the bore, it is in alignment with the AXIS not the bore unless the bore was perfectly straight which it will not be. Again how can the bore be turning true and square with the machine tooling if the indicator rod will not center along it's entire length? This may not be very important when chambering using a piloted reamer that will follow the bore but it would be extremely important if chambering with a boring tool or when crowning. Again HOW can the bore possibly be square to the crown if the indicator rod will only center at one indicated point? How can the bore not be wobbling if the indicator rod is (as it will be if both bore ends are centered)? Remember that indicator rod is a continuation of the bore at the muzzle and any out of center indication along it's length will be simply an extension of the same error for the bore, it can't be anything else!
I have seen this argued back and forth a bunch of times and I doubt those who are so set in the way they have been doing it are going to be convinced either way but the real problem is that the advocates of "center both ends" fail to distinguish between the true bore and the setup spin axis. Your description above is an example, what you describe will certainly align and square with the indicated AXIS but not the actual bore. It will be centered at ONLY the two indicated points but it will not be parallel to the bore anywhere as shown by the wobbling indicator rod.
How can the bore possibly be in true alignment with any machining operation if the indicator rod will only indicate centered in one spot? Don't confuse bore with axis, unless the bore is perfectly straight they can never be the same!
Picture that archer's bow example, the principle is exactly the same and the exaggerated example changes nothing, it only makes it easier to see. If that bow was to be centered using the method you describe any subsequent machining would then be done based on and parallel to the string which would be a representation of the axis, sure the chamber and crown would be CENTERED (only at the exact indicated points however) but what happens to parallelism and squareness? A gross exaggeration of course and since fortunately most bores are close enough to straight so that centering both ends usually works Ok but why do it that way when it can be even better?
Also too having the chamber aligned with the bore as you said I again ask HOW can it be truly aligned if the indicator rod will only center in one spot which is an indication that it is not aligned itself? Centering and alignment are two very different things.
Last edited by oldred; 08-23-2018 at 10:43 AM.
Statistics show that criminals commit fewer crimes after they have been shot
There are a multitude of methods to chamber a barrel blank. And an infinate number of ways to ruin even the best barrel with each and every one of those methods.
There is no one single method that is or has been used to chamber and crown benchrest winning barrel blanks. The outcome is largely dependent upon the person doing the chambering and the barrel blank itself.
Why can't we discuss this in a civilized manner without resorting to anger? I thought we were debating the merits of two WELL KNOWN methods of doing this, I didn't just dream it up myself!
No it aligns the last few inches of the bore! Whether it makes sense yet or not that rod is in true alignment with the actual bore (explain how it could be otherwise?) and it will remain in alignment regardless of how you dial it in. If that rod is wobbling then the bore absolutely has to be wobbling at that point also because the rod is an extension of the bore! And no I am not "painting a picture that rifle bores are crooked as a snake" but that wobbling indicator rod with both ends centered is proof they are not straight either!
I have said more than once it is an error so small that either way works but one way works better!
By dialing in both ends so that the rod will indicate true along it's length you will have aligned the last few inches of the bore so that crowning or any other machining operation will be truly square with the bore, if that rod will not center along it's length then any machining operations, while being pretty well centered, will still not be square to that wobbling bore and the bore WILL wobble just as much as the rod will because that rod is an extension of the bore and a positive indicator of the bore alignment at that point, instead of getting mad and just asking me why some other people do it your way why don't you show me where I am wrong? If you can explain how that bore can be cut true square at the muzzle when a crowning operation is performed with the rod, and thus the bore also, wobbling then please do. Please explain how the bore can possibly be in any better alignment than that wobbling pin? Which is going to be true square when cutting the crown, with the bore wobbling at that point as indicated by the wobbling pin fitted into that bore or a bore that does not wobble at the point of machining as when indicated by the rod running true along it's entire length? Both methods will be centered but one way will have a wobbling bore at the point of machining while the other will not.
That rod, if fitted properly, does not lie and if it is wobbling then so is the bore, again HOW can it be otherwise? Explain how that perfectly straight rod inserted into the bore could wobble while the bore would not? Obviously if the rod will not center in more than just that one spot then it must wobble so if that straight rod wobbles while inserted snugly into the bore how can the bore be truly square to any machining operation?
Last edited by oldred; 08-23-2018 at 10:23 PM.
Statistics show that criminals commit fewer crimes after they have been shot
Ok again you try to avoid the logic by pointing at the fact what you do is common, that changes nothing and ignores the fact that what I am talking about is also used by others, again I didn't just dream this up!
What I have said has conflicted with what you have taken for granted obviously without really looking at it and apparently you can't explain anything I have asked that would show where I am wrong about this. I explained my points and all you can say is no that's wrong because other people do it my way, well other folks also do it the way I am describing and that's how I leaned of it! Until not long ago at all I too did it your way but that wobbling indicator rod didn't make sense to me, I even brought it up here on this forum less than a couple of years ago, that's when I talked with the 'Smith who explained it so clearly using that archers bow example.
Think about this and then tell me where I am wrong,
Ok what is wrong with this? A perfectly straight indicator rod (range rod) is inserted into the bore and being an extremely snug fit it MUST follow the path of the bore at that point, can we agree on that? If it extends out at least two inches (for example) but will indicate center in only one spot as close to the muzzle as practical and will show increasing run-out the farther the indicator moves out then quite obviously it will be wobbling on that end, can we agree on that since that is the normal condition if both ends of the bore are centered in the lathe. Now if that straight rod is wobbling on that outer end, and it normally will be when both ends of the bore are centered, then how can the inside end of that perfectly straight rod extending into the muzzle not be wobbling the same amount on it's other end? Since the rod is a true indicator of the bore's path at that point (or maybe you can explain how it wouldn't be) then quite obviously the bore must be wobbling exactly the same as the rod, if the rod wobbles then so MUST the bore wobble the same way! No? Then please explain how it couldn't be, if it isn't I honestly would like to understand the mechanics of how that could be!
Now if we use the outboard end of the barrel/bore to dial in that bore while in the lathe so that the rod in the muzzle end (for a crowning operation for example) will be indicating true all along it's exposed length it obviously will no longer be wobbling. Since it is no longer wobbling on the exposed end and it's perfectly straight then obviously neither is the end inserted into the barrel wobbling now, if it's not wobbling then just as obviously neither is the bore!
Which setup will cut a more true square-to-bore crown, the one that is wobbling or the one that is turning straight and true at that point?
Again, let's look at the exaggerated example of the archer's bow, greatly exaggerated yes but still a good example of the principle involved and is exactly the same as what's happening on a smaller scale with even normal within tolerance run-out in a bore.
The bow itself would be representative of the less than perfect bore and if both ends were then centered in a lathe using indicator rods on the ends then the string would be a perfect example of the turning axis while in the lathe. Centering both ends of that bow is EXACTLY what we would be doing by centering both ends of a less than perfect bore, picture that bow wobbling around that straight axis and then chamber/crown/whatever squared relative to the straight spin axis, sure both ends may be perfectly centered but look at how they would be cut relative to the actual bore where it counts! Now if we allow the outboard end of that bow to move to a point that allows the last few inches of the other (work) end to indicate true along the entire length of an indicator rod then any machining done will be relative to the bore rather than having to run askew of the bore while having to follow the axis it is dialed in relative to if both ends are centered! For sure that bow is an extremely exaggerated example but again the principle is exactly the same and it should serve to illustrate the difference between the spin axis and the actual bore since a bore will never be true to that axis. By dialing in both ends as closely as possible we are simply centering the ends of the bore on the axis and ignoring the ANGLE of the bore at the point of machining and that wobbling rod is a certain indicator of a wobbling bore.
If a wobbling indicator rod does not indicate a wobbling bore then please explain why it won't!
Last edited by oldred; 08-24-2018 at 06:07 PM.
Statistics show that criminals commit fewer crimes after they have been shot
Of course, a wobbling pin indicates the bore is wobbling. The objective is to adjust the hold on the barrel so the pin does not wobble anywhere along it's length. At that point the axis of the barrel at the other end may be somewhere else. So What? Indicate one end,then machine the chamber or crown. Turn it around and indicate/machine the other end. The big question is, is the barrel so crooked that threading after indicating the bore at one end will have the other end pointig way off to one side?
I was taught to cut centers in each end with a piloted center reamer and doing the threading between centers. The the steady rest was used to hold the muzzle while crowning. Then chambering was done with the steady rest riding on the threads. Thtat was in 1975, before benchresting was so popular all across the country and was not mentioned by any of the instructors at CST. For hunting rifles it seemed to be entirely adequate. For benchrest, more attention to alignment seems to be required. A picky person might want to get centers cut as accurately as possible, then carefully check the exterior of the barrel for run out all along it's length. Also sight through the bore for any indication of run out and determine if the barrel is suitable for it's intended use. Don't ask me to do that as I can't see that well or want to spend that much time doing that. Since I only hunt or shoot for recreation, I will use barrels by manufacturers generally recognised as making good product. If I wanted extreme accuracy, I would expect to pay much more for a barrel from one of the premier barrel makers and would take much more care in the machining and fitting of it.
All that really matters is that the targets reflect what the resired results were, doesn't matter how you got there so long as you can afford it.
One way to "see" if a bore is straight and true is to use a series of pins in different lengths. a 2" long pin at .xxxx that slides thru the bore freely then a 4" long pin at the same dia and last a 6" long pin at the same dia. if the bore isn't straight then the longer pins will bind due to the curve.
In reality deep hole drilling when the drill wander it seldom comes back but continues and one end is off center. size can vary due to heat and chip load build up. Stress build up also contributes to run out.
The advances in stress relief of the blanks ( almost all top end barrel makers stress relieve the stock before starting and when finished blank) has made big improvements in blanks. The improvements made in blending and alloying materials also improved things. The newer computer controlled deep hole drills with the peck cycles, coolant thru the drill and once drilled thru the blank, Higher coolant pressures and better cutting fluids all aid in controlling heat build up chip removal and tool life. The right cutting fluid/coolant will carry most of the heat out and flush chips out. Last is the peck cycle that drills the barrel in .020-.030 steps or there abouts, this keeps chips small and improves the fluids ability to flush them out.
That about sums it up
When I first started doing this it seems everyone and their uncle was telling me to get both ends of the barrel/bore centered as closely as possible but I was also warned to indicate the range rod as close to the bore as possible, that was the only way to get everything perfectly aligned! When I did that and found that the rod would tend to run out of center at an ever increasing rate the farther outboard I went it was apparent it was wobbling and thus the bore had to be wobbling also. This just didn't make sense and when I asked about it most everyone was telling me it didn't matter don't worry about that, what's important is to get BOTH ENDS centered as close as possible. I kept asking myself just why centering both ends was more important than that wobbling pin (and thus the bore)? I did one barrel with that both ends centered setup but that wiggling pin just didn't make sense to me nor did the importance of centering the outboard end of the bore make any real sense either! I looked more into it and that's when I learned that what I was asking about is actually a common way of setting up a barrel in a lathe and is actually the more accurate way of doing it, that made a heck of a lot more sense to me than that wiggling indicator rod and after having that discussion with the gun smith who used that archer's bow example it became quite clear to me.
Statistics show that criminals commit fewer crimes after they have been shot
To me the chamber should be perfectly aligned with several inches of bore ahead of it.
Then we ask what is the best way to achieve that, rod that barely slips in seems like a good way, I think some make them that take reamer bushings too.
One person I talked to described a device he had made to reach up inside the barrel and simply indicate it's ID...a long indicator tip does not work so well for this because if you double the length of the tip you halve the sensitivity of the indicator.
He described the mechanics of how his lever worked...that was what it was a lever built so as to not have any slop in it.....it worked on a 1:1 ratio so that the indicator reading the other end of the lever was measuring exactly the motion at the end that was touching the bore.
But anyway.....for lots of purposes just aligning muzzle and breech end may be just fine...sure there is some error because no bore is a straight line, and a barrel that has been BENT into a straight line after rifling is NOT a good thing....so just leave it alone as made, indicate the muzzle and breech, live with maybe .015" curve in 26" in the bore, do the math on what that error is over the length of the chamber. If I do the math on that a 26" barrel with .015" curve to the bore aligned muzzle to breech would have 0.000874" difference between a 22PPC case and the bore axis....less than .0001", IMHO the indicating methods used to try to align the last 3" of core may stack up that much error.
What would be interesting as a blind test would be to have say 4 different "master smiths" align the same barrel for chambering...and somehow lock in their alignment, say turn a 1" section of the barrel straight, and compare their results in a blind test.
Some Folks will pre drill the chamber, re indicate the bore "up in there" then single point bore the hole at the same angle as the case body.
As to crowns being perfectly square and concentric, yes that is the desired result, BUT in some of the many "ballistics by the inch" tests they chop rifle barrels off one inch at a time and crono, and some guys shoot groups along the way, and a plain chop sawed muzzle (they usually cut not friction saw) often shoots pretty good...not that we would ever DO it that way.
The BR boys are probably only wasting powder and bullets on barrels that shoot in the .03 range maybe, conditions and such prevent that from happening much...and many garden variety shooters do not learn to read wind and learn to make the gun ride the bags, and do not have BR type stocks....so will never see that level of accuracy. The number of folks who only shoot 3 shot groups will show you who really wants to see how a gun shoots...and who wants to show a nice group. But the way they find those good barrels is maybe having them mapped first for twist and bore size (most buttoned barrels gain or lose some twist...the one that lose are thought to be less accurate) then having them fitted and chambered, and shooting them. Tony Boyer if I recall right said that one of his most accurate barrels ever was one of the most crooked one he ever tried to use
Bill
Both ends WHAT a player
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