Bill Leeper
New member
"never been abused" is probably an understatement. The previous owner would have probably wiped a chip off the ways as soon as it hit! Regards, Bill.
Curvature in barrels and chambering
- Thread starter chino69
- Start date
P
PPP MMM
Guest
Indicating both ends of the bore
By using my carbide tool that was once described elsewhere on this forum where I can indicate and measure both ends to 0.01mm and 150mm deep at the same time I've found both. Barrel bores that are curved as a banana and the more common barrel bores that have a "sudden" change of direction.
Shoot well
Peter
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By using my carbide tool that was once described elsewhere on this forum where I can indicate and measure both ends to 0.01mm and 150mm deep at the same time I've found both. Barrel bores that are curved as a banana and the more common barrel bores that have a "sudden" change of direction.
Shoot well
Peter
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Roger rodbolt
Guest
Dennis,
I smiled when I saw your Rockwell and setup. My ll"x37" also wears the original paint with very few miles. I use a wrap of brazing rod around the barrel in a both a 3 jaw and 6 jaw Buck chuck that have the "Adjust-Tru" feature which allows light jaw pressure on the brass rod then the backplate adjusts independently of the jaws to center the bore. I believe mine is a 1971 model. It runs smooth on 3 phase and is deceptively rigid.
I smiled when I saw your Rockwell and setup. My ll"x37" also wears the original paint with very few miles. I use a wrap of brazing rod around the barrel in a both a 3 jaw and 6 jaw Buck chuck that have the "Adjust-Tru" feature which allows light jaw pressure on the brass rod then the backplate adjusts independently of the jaws to center the bore. I believe mine is a 1971 model. It runs smooth on 3 phase and is deceptively rigid.
B
Bill Myers
Guest
I have a Collet chuck & a complete set of 2J collets to fit the Rockwell,I think that they are LOO.If any one needs them,I will make you a great deal.There are 32 collets in the set & the chuck is a hand wheel type. BILL
Butch Lambert
Active member
jackie schmidt
New member
Peter
I do not know how many Benchrest BarrelsI have chambered in the past 10 years, but they are numerous. I have never seen one with a single plain bow in it such as a bannana exibits.
I would figure the odds of a Gun Drill doing that would be pretty far fetched. Not impossible, just far fetched......jackie
I do not know how many Benchrest BarrelsI have chambered in the past 10 years, but they are numerous. I have never seen one with a single plain bow in it such as a bannana exibits.
I would figure the odds of a Gun Drill doing that would be pretty far fetched. Not impossible, just far fetched......jackie
I've been experimenting with chambering methods for the last few months...I don't have the experience most of you do, but I've been learning and finding out what works for me. What really bothered me at first was what I saw when using the PTG range rods. I would use an indicator to dial in the muzzle and chamber both within -.0002". When double checking with the range rod, right at the chamber end it was right on....then I'd move the indicator 2-3" away from the barrel and indicate on the rod and it was over .003 out (or more). Either the range rod is bent or the bore is not straight (or I suppose there's slop in the bushing, but I had a good fit...much less than .003!). I don't have a long stem indicator to reach way up in there so at this time I haven't drilled the chamber, indicated the throat, then bored the hole true...just didn't have the tooling.
So after reading about Gordy's method and watching his video I made a couple indicator rods like he uses and tried that on the next barrel. I still didn't drill and bore, BUT I was able to get that first 3" or barrel close to dead true using that rod. This was a great way for me to get around not having an indicator with the 2+" stem and still being able to dial in the throat area. That bore seemed to be out up to 4 thou or so in the first 3 inches, and after dialing the bore in on both sided of the pivot point in the chuck (it took about 4 or 5 'back and forths') the runout was within two tenths for the first 3+". Isn't that what we're striving for??? a dialed in throat area with a chamber and beginning of a bore that are all in-line with each other???
Anyway, after dialing that barrel in, I did measure the run-out at the muzzle end and it was less than ten thou. I think you could get a lot more than that and it wouldn't matter, but I'm mainly interested in building accurate rifles for hunting and some long range applications, so like Gordy I also indexed the high side to the top of the action. This required threading before chambering, but after the tenon was turned and threaded, nothing had moved as I re-indicated things in at that point.
The chamber turned out great in my opinion, and hopefully in a few weeks I'll be able to shoot that 30-284 and really see what it will be capable of.
This is just my (limited) experience, but I consider myself a faily observant fellow, and I feel this IS a great method for a barrel that has a bore that is 'out a bit'. I may not use it every time, but after getting a barrel dialed in and checking with a range rod, if the end of that rod is rotating in a visible circle, you can bet the muzzle won't be centered dead true when I get around to the chambering as I'll use the long indicator rod and Gordy's method.
So after reading about Gordy's method and watching his video I made a couple indicator rods like he uses and tried that on the next barrel. I still didn't drill and bore, BUT I was able to get that first 3" or barrel close to dead true using that rod. This was a great way for me to get around not having an indicator with the 2+" stem and still being able to dial in the throat area. That bore seemed to be out up to 4 thou or so in the first 3 inches, and after dialing the bore in on both sided of the pivot point in the chuck (it took about 4 or 5 'back and forths') the runout was within two tenths for the first 3+". Isn't that what we're striving for??? a dialed in throat area with a chamber and beginning of a bore that are all in-line with each other???
Anyway, after dialing that barrel in, I did measure the run-out at the muzzle end and it was less than ten thou. I think you could get a lot more than that and it wouldn't matter, but I'm mainly interested in building accurate rifles for hunting and some long range applications, so like Gordy I also indexed the high side to the top of the action. This required threading before chambering, but after the tenon was turned and threaded, nothing had moved as I re-indicated things in at that point.
The chamber turned out great in my opinion, and hopefully in a few weeks I'll be able to shoot that 30-284 and really see what it will be capable of.
This is just my (limited) experience, but I consider myself a faily observant fellow, and I feel this IS a great method for a barrel that has a bore that is 'out a bit'. I may not use it every time, but after getting a barrel dialed in and checking with a range rod, if the end of that rod is rotating in a visible circle, you can bet the muzzle won't be centered dead true when I get around to the chambering as I'll use the long indicator rod and Gordy's method.
Jim Borden
New member
Added piece of input
When using the Gordy method--make sure that whatever you hold the range rod in at the tailstock is on the centerline axis of teh lathe--if it is not--you will not be lining up the first two inches of the bore with the lathe axis--but with an axis that is angular to the lathe.
Jim Borden
When using the Gordy method--make sure that whatever you hold the range rod in at the tailstock is on the centerline axis of teh lathe--if it is not--you will not be lining up the first two inches of the bore with the lathe axis--but with an axis that is angular to the lathe.
Jim Borden
Niccolo M.
Member
This works for me
I use the Indicator Rods from PTG. They work great but you need two .0001 test indicators at the same time to use one correctly, one near the barrel at the head stock and the other at the right end of the Indicator Rod towards the tail stock. I adjust the run-out of the one closest to the chuck with the set-tru feature of my PBA six jaw. I adjust the run-out of the right end with the spider on the out board or left end of my lathe spindle. I could care less if the muzzle is running out because to get both ends dialed in you would have to bend the barrel; they are not drilled straight, period. The Rods use bushing on the tip that you purchase in .0002 increments and the Rods have a taper to align the body with. After I get things straight, I taper bore an undersize pre chamber, move the rod to where the throat will be and check things again and adjust as required. I then finish taper boring my pre chamber to re-true it and then ream the chamber with a finish reamer using the same bushing that I used on the Rod and pressurized cutting oil flushing through the barrel. It works for me; I like Gordy’s set up and method because it saves the re-indicating step. I like my method because it lets me QC the process all along the way. Oh yea, I turn and thread the shank .002 oversize and bring it down to size after the chamber is finished. I use full thread form thread cutting tooling from Kennametal so the root and crests are cut at the same time, works great. I use the full thread form tooling when truing the internal thread of receivers too, makes that job a no brainier.
Just don’t kiss the shoulder during the re-thread operation!
Nic.
I use the Indicator Rods from PTG. They work great but you need two .0001 test indicators at the same time to use one correctly, one near the barrel at the head stock and the other at the right end of the Indicator Rod towards the tail stock. I adjust the run-out of the one closest to the chuck with the set-tru feature of my PBA six jaw. I adjust the run-out of the right end with the spider on the out board or left end of my lathe spindle. I could care less if the muzzle is running out because to get both ends dialed in you would have to bend the barrel; they are not drilled straight, period. The Rods use bushing on the tip that you purchase in .0002 increments and the Rods have a taper to align the body with. After I get things straight, I taper bore an undersize pre chamber, move the rod to where the throat will be and check things again and adjust as required. I then finish taper boring my pre chamber to re-true it and then ream the chamber with a finish reamer using the same bushing that I used on the Rod and pressurized cutting oil flushing through the barrel. It works for me; I like Gordy’s set up and method because it saves the re-indicating step. I like my method because it lets me QC the process all along the way. Oh yea, I turn and thread the shank .002 oversize and bring it down to size after the chamber is finished. I use full thread form thread cutting tooling from Kennametal so the root and crests are cut at the same time, works great. I use the full thread form tooling when truing the internal thread of receivers too, makes that job a no brainier.
Just don’t kiss the shoulder during the re-thread operation!
Nic.
Butch Lambert
Active member
Jackie,
I guess that I am still messing up barrels!
Butch
I guess that I am still messing up barrels!
Butch
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WillBird
Guest
One thing many people never really grasp.....and it is a help I think if you can grasp it 
.
NOTHING is ever completely round, flat, true, parallel, square, spherical, So this means there is no such thing as a straight barrel.
I agree 100% with crowning the barrel square and concentric to the last 2" of barrel, and chambering it square and true with the 2" of barrel ahead of said chamber.
Another thing to ponder on....if the ID of a barrel is not one straight line from muzzle to breech, then the OUTSIDE of the barrel cannot possibly be concentric to the inside over the whole length...and there is NO practical way to correct THAT.
As a tool and die maker I HAVE seen holes drilled with Titex parabolic drills that sure appeared to be curved, 1/8" holes drilled 8" long, that walked about 3/4". The only cause we could determine for that was a drill that ran out....IE wobbled about 1/8"
Again as a tool and die maker I have seen cases where there was a difference in hardness of a material, and this causes twist drills to walk towards the softer metal. Also I know that the steel round stock that a barrel is made from started out as a much larger dia billet or pig that was much shorter, then it was rolled out to a longer length/smaller dia, and that the resulting bar still has all the flaws present in the pig or billet. So what I'm saying...is that if the metal in a barrel blank is not consistent, this could make the drill walk in a curved action. In real life maybe this results in a buildup of pressure, then an incremental "walk" such as others have described.
Bill
.NOTHING is ever completely round, flat, true, parallel, square, spherical, So this means there is no such thing as a straight barrel.
I agree 100% with crowning the barrel square and concentric to the last 2" of barrel, and chambering it square and true with the 2" of barrel ahead of said chamber.
Another thing to ponder on....if the ID of a barrel is not one straight line from muzzle to breech, then the OUTSIDE of the barrel cannot possibly be concentric to the inside over the whole length...and there is NO practical way to correct THAT
.As a tool and die maker I HAVE seen holes drilled with Titex parabolic drills that sure appeared to be curved, 1/8" holes drilled 8" long, that walked about 3/4". The only cause we could determine for that was a drill that ran out....IE wobbled about 1/8"
Again as a tool and die maker I have seen cases where there was a difference in hardness of a material, and this causes twist drills to walk towards the softer metal. Also I know that the steel round stock that a barrel is made from started out as a much larger dia billet or pig that was much shorter, then it was rolled out to a longer length/smaller dia, and that the resulting bar still has all the flaws present in the pig or billet. So what I'm saying...is that if the metal in a barrel blank is not consistent, this could make the drill walk in a curved action. In real life maybe this results in a buildup of pressure, then an incremental "walk" such as others have described.
Bill
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frwillia
Guest
Well, I'm a newbie and jumping into the deep end of the pool, and I should know better, but you are a knowledgeable guy so I'm going to ask you (and any others who might have an opinion
) a question in search of understanding. First, because I'm really new here, some background:
You have made the banana comment before and after some studying my confusion is that I don't see what being only banana shaped as opposed to the bore wandering around has to do with anything related to choosing a chambering alignment method. Wandering around is the general case, banana shaped is a specific subset of wandering around.
Alas, I'm handicapped by being an engineer and also having used a lathe more or less constantly since 1950 (when I was 8 years old) and a mill as well for the last 15 years. I'm of the opinion that every engineer should be required to own a lathe. In fact I still have that same lathe, a lovingly used 9" SB Model A with 4' ways and about every attachment ever made for one) which arrived new and covered with cosmoline in my Dad's basement in 1950, in my shop now.
My other lathe is a 12 x 36 gear head import, Andes is the name on it if it matters, and that is the one I'll be using for chambering because I can work through the headstock with it.
Since leaving CA and moving to PA (I was raised on a farm in Michigan) I've gotten back into shooting in general, varmint shooting and mid range (600 yards and under) target shooting. Having a lot of fun with it. have made several good friends at ranges. I shoot at Shippensburg Fish and Game most of the time. Excellent rifle range, lots of good folks.
I'm in the study and tool making phase of preparing to chamber rifles as one of the ways of enjoying my retirement from 35 years of aerospace engineering. That was 35 years of never doing the same thing twice, and mostly figuring out how to do things that had never been done before. It was an E-ticket ride.
Back to the present. I don't have infinite resources which the current economy has diminished more than a little, so I want to make really good choices in tooling up to build some custom rifles for myself. The building includes truing actions and chambering barrels.
I've been all over various forums reading the threads on aligning a barrel for chambering with considerable interest. I've learned a lot. Been making tooling. In fact I've compiled a 110 page book of information by cutting and pasting stuff from the WEB into a Word file. I gave a copy of it to a friend who has been doing some chambering and he said that he learned a lot from it even after 8 years of chambering, so there is a lot of good information in this and other forums (where many of the same good folks post).
There appear to be two ways of aligning for chambering that are frequently used, and which, if one understands the differences, are in fact profoundly different. There are accomplished and successful smiths who use one or the other, or possibly in some cases, both (though not on the same barrel).
My interest is based on the well established fact that the bore centerline measured at points in the barrel will wander around more or less at random in the barrel. Gun drills do that. It's a fact. They don't make either bananas or straight lines except by coincidence. They pretty much wander around with in limits determined by the bit geometry, counter rotation of barrel and bit, material variations, and who knows what else. Definitely a chaotic process within some limits.
Given the bore is in different places along the length of the barrel, and has to get from one location to the other, it follows that the bore has to be at a more or less constantly changing angle with the end to end barrel centerline moving between these points - and there is no reason for it to be aligned in the barrel at the ends any more than it is some place else. How much the bore centerline varies from the end to end barrel centerline seems to be a question, but it will doubtless vary from a few to several thousandths of an inch in all but a few barrels.
Doesn't matter if it is banana shaped or wanders around for my purposes. An approach that deals with one, deals with the other, wandering around being the more general case.
Near as I can tell, Gordy Gritters approach to aligning the barrel for chambering and crowning deals with the reality of the bore wandering around by attempting to align the axis of the chamber with the axis of the bore at and just beyond the throat. Alignment of the lathe axis with the axis of the bore in the location being machined being the crucial feature of the approach at the breech end.
This alignment is thought to be desirable because it assures that, if the chamber is well cut, the bullet strikes the throat symmetrically with contact occurring in a plane that is as close to orthogonal to the bore axis as it can be done within the limits of the machine, reamer quality, and skill of the person doing the setup, and also has the bullet traveling along the bore axis (where ever it is pointed) at that location. At the muzzle, Gritters approach results in a muzzle crown exit plane that is as close to orthogonal to the axis of the bore at that point as it can be.
The reasoning behind this approach is apparently that it should create the best chance for the rifle to shoot small groups because the bullet experiences the most symmetry at its entrance to and exit from the bore. Gordy has stated in other threads that after he adopted this approach, his percentage of really tiny grouping barrels went up significantly.
There are two down sides of this approach that I can see. The first is that doing this in a steady rest is quite a bit more difficult than doing it through the headstock. It can be done, but it required a spider equipped steady rest which isn't all that common.
The other is that absent some special effort, the bore could be pointing pretty much any which way at the muzzle and result in a bullet path that starts out in a direction other than aligned with the centerline of the receiver. It should follow that path with great consistency, but it will not be a direction that is necessarily aligned with the receiver, which is the frame of reference because the scope is mounted on it, and it may cause issues with scope mounting.
In fact the misalignment is probably only a matter of degree, since there is no reason for the bore to be aimed in the direction of the receiver centerline using either method, thought it may be closer using the method described next.
That said, the misalignment can be accepted or an attempt can be made to manage it by having it point up in a vertical plane along the intended path of the bullet that is aligned with the receiver in order to avoid more severe than normal scope mounting issues. Clearly if it is to be managed, having it in the vertical plane is the best place to put it.
In fact, as an aside, it could be argued that it is a good idea to align the bore at the muzzle exit to fall within a vertical plane aligned with the receiver regardless of chambering method because it reduces the magnitude of non-wind caused distance related azimuth adjustments in the scope. Drawing a picture of a barrel with the bullet exiting at an angle to the left with a line from the breech to the target shows that as range changes, the scope windage setting would have to change. But that is another subject for another day.
The other commonly used approach is to indicate a point along the bore axis to be centered near the throat region of the chamber to be and another point on the bore axis at the muzzle. This results in the lathe axis being aligned with nothing in the barrel but with a virtual centerline between the two points instead of something in the barrel, like the axis of the bore. Using this approach, the lathe axis isn't aligned with the axis of the bore in the throat region other than by chance, nor is the muzzle crown machined using the same principles orthogonal with the axis of the bore at the muzzle other than by chance. In other words, the two painstakingly centered alignment points at the far ends of the barrel create a virtual bore centerline between the breech centered point and the muzzle centered point that is aligned with the lathe axis and nothing else in the barrel, except by coincidence.
I'm asking you this question, though others will doubtless feel free to comment as well, and I welcome their input, because when reading other posts, you have lots of experience, and your approach as I understand it is to center the muzzle and a location in the bore where the throat is to be located and proceed from there. This is the second approach described above.
The tooling is different - in one case I would need a long armed indicator, in the other some some called "Grizzley rods" and bushings. I can make the rods, I'll buy the bushings - I don't fool myself that I can make a set of bushings that differ by only .0002" with any certainty.
OK, finally, my question: Assuming symmetry of throat and crown interaction with the bullet is desirable, and only happens by chance using the muzzle/breech two point approach, I am curious to know what the benefit is that makes this approach the better one to use in-spite of that?
This is a real question. I may have missed something and I am very interested in the answer.
Thanks
Fitch
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frwillia
Guest
R
Riflemeister
Guest
The post by frwillia above is the most concise presentations of the problem I have ever read on this forum. I'll bet with the clarity of thought you put toward this issue you are one helovan engineer.
The way it's presented almost makes the case for Gordy Gritters' Grizzly rods indicating in the throat and the position where the pilot resides and indexing the high side. It might be a little more elegant to use a long indicator to refine the setup and of course a pre-bore would be a necessity. It sure does address the range rod shortcoming of indexing two points, one of which may or may not be the throat. It also addresses the issue of the bore intercept angle that is ignored by indexing the throat and muzzle.
It would be nearly impossible to do a meaningful test to compare the results of the various methods. Most results would be anecdotal rather than definitive. I'll leave it to you smart guys to figure out how to test the various chambering setup methods. I'm willing to concede that my previous reliance on range rods was not the best answer. I just rescued that 280 Ackley barrel by making it into a 7 Mag using the indicate the throat and the muzzle method and runout all the way up the chamber and throat was under .0002" the whole way, but I'm still troubled by the bore intercept angle with that method.
The way it's presented almost makes the case for Gordy Gritters' Grizzly rods indicating in the throat and the position where the pilot resides and indexing the high side. It might be a little more elegant to use a long indicator to refine the setup and of course a pre-bore would be a necessity. It sure does address the range rod shortcoming of indexing two points, one of which may or may not be the throat. It also addresses the issue of the bore intercept angle that is ignored by indexing the throat and muzzle.
It would be nearly impossible to do a meaningful test to compare the results of the various methods. Most results would be anecdotal rather than definitive. I'll leave it to you smart guys to figure out how to test the various chambering setup methods. I'm willing to concede that my previous reliance on range rods was not the best answer. I just rescued that 280 Ackley barrel by making it into a 7 Mag using the indicate the throat and the muzzle method and runout all the way up the chamber and throat was under .0002" the whole way, but I'm still troubled by the bore intercept angle with that method.
The written language is a crude form of communication, but I'll try to give you my answer as I see it.
The two perpendicular vectors you refer to, one the bullet, the other is the bore. The goal is to machine a chamber that is orthoganal to the bore axis, in the area of the throat. Lets all agree on that.
Your rationale cannot be argued with mathmatically...you are correct.
But, in practical terms, you are wrong...because we are forced to live in a world of relatively crude tooling....in the home shop especially.
There are lots of terms for it....some call it stacked tolerance, some call it dilution, it's all the same basic problem a machinist faces. We can only indicate a workpiece within the abilities of the instruments. What we lose in minute angular alignment, we gain in some multiple of accuracy in radial alignment, by DIRECT indication of the throat area, with a .0001" indicator.
In simple terms, the range rod is a long sloppy tool, on which assumptions are made. A 10ths indicator is a precise tool, with a lot less chance for error. i.e. it is more repeatable.
Also, if a bore has a shift, bend, whatever in it, of .001" over 6 inches...what is the angle? Yes you can calculate it, but there will be several decimal places. Its a tiny gain.
Gordy has a hypothesis, not a theory. Until it can be quantified through analysis of variance, or some other practical means, I would say he cannot correlate his increased amount of accurate rifles to the assumed angular alignment of the bore to chamber
Try this.....
Take a benchrest grade barrel and indicate it in the lathe 5 times using both methods. 10 times total. Remove the barrel from the lathe completely each time.
Check muzzle runout at the spider, and record it all 5 times using Gordy's methods. also mark the index point on the muzzle with a sharpie.
Let us know which method is more repeatable. Repeatability is the cornerstone of accuracy.
Ben
MColeman
Club Coordinator
Darned if I remember.
In fact, I don't even remember posting this.I may be letting myself open to a lot of criticism here but I don't think going to all these measures is giving any observable accuracy in an agg. We may take comfort in knowing that we've done everything we can but all you have to do to negate everything is miss one reverse and have a flier turn a .1xx into a .4xx and you're toast.
I think that it's more important to learn 1. when to start your group and 2. learn to tune a barrel and 3. learn how to read conditions than it is to get a throat indicated in to less than .00000000000000000001 inches, at least in short range benchrest. Can't say about 1,000 yard shooting. I can't afford the wind flags for that.
MColeman
Club Coordinator
After reading Fitch's excellent post a question popped into my mind
If a gun drill wanders while drilling just how much does it 'wander' and, assuming that it does is that not negated to some degree when they ream the bore? A reamer, being fluted for, say, an inch only cuts really on the bevel on the end but how much flex can the reamer have while it's cutting?
So long as the chamber and throat is perpendicular to the bore it really doesn't matter where the bore goes between the throat and the muzzle, within reason, of course. That's why Gordy isn't concerned with the muzzle when he's chambering. He wants the 'high' point to be at 12 o'clock in relation to the action simply because it will give the 1,000 yard shooter a couple of minutes of more elevation. He said that is the only reason to be concerned with that. It's of no concern to us point blank shooters.
If a gun drill wanders while drilling just how much does it 'wander' and, assuming that it does is that not negated to some degree when they ream the bore? A reamer, being fluted for, say, an inch only cuts really on the bevel on the end but how much flex can the reamer have while it's cutting?
So long as the chamber and throat is perpendicular to the bore it really doesn't matter where the bore goes between the throat and the muzzle, within reason, of course. That's why Gordy isn't concerned with the muzzle when he's chambering. He wants the 'high' point to be at 12 o'clock in relation to the action simply because it will give the 1,000 yard shooter a couple of minutes of more elevation. He said that is the only reason to be concerned with that. It's of no concern to us point blank shooters.
F
frwillia
Guest
Thanks for the thoughtful response. Much appreciated. I just read through this reply - didn't mean to make it so long. I keyboard really fast.
Uh, yes, I think. I agree with what I think you intended to say.
In the name of precision (yes, language is a tough way to communicate) I'd like the bullet path and bore to be coaxial vectors, the same, at the pont of entry (throat) and exit (muzzle).
With that in mind, I could agree that the goal is to machine a chamber that is aligned with the bore axis at and for at least a bullet length beyond the start of the lands in the throat, and a muzzle crown the plane of which is orthogonal (at all points perpendicular) to the last bullet length of the bore axis at the muzzle.
That makes my head hurt, but I think it is correct.
I understand what you are saying, I'm not sure I agree with it in general but let me think for a minute ... OK ... lets do s thought experiment. Same barrel in both cases. The assumption is that the bore and the average centerline between throat radial location and muzzle radial location don't align where the chamber throat and crown will be located. I think we both agree that misalignment is more likely than not and only a matter of degree as a function of the barrel makers triumph over the variety of variables involved.
Suppose you can absolutely perfectly, with zero error, center the measured point at that selected location along the barrel in bore radially right on the spindle axis. If you do, you will still have the angular error between the spindle axis and the local bore axis that occurrs by chance. What ever reduction in group size occurrs as a result of the angular error can't be reduced even by unachievably perfect centering.
If, on the other hand, you could align the chamber centerline with the bore center line for a short distance, say a bullet length, past the throat, that will probably result in the most favorable bullet entry into the bore.
Your reply is based on our being able to do the first measurement more accurately than we can do the second, and for that reason the first measurement will result in the most accurate barrels averaged over time, and thus represents the best approach.
Could be. Can't rule it out with the data in hand, though Gordy thinks he has a different answer. See discussion after the next quote for more on this.
The down side to it is there is no chance to get better using the first approach. The best it can be will always be short of the best the barrel can be other than by chance.
Using the second approach, there is the chance to develop tools and instrumentation approaches that will result in improvement which will at least have the chance of improving shooting performance to what ever extent it can be improved by aligning things correctly. There is real appeal to following an approach that will respond to improvements as we get better.
That would be ~0.57 MOA if I did the math right.
You bring up an interesting point. I wonder about sources of error. Using Gordy's method, with fitted pilots (in increments of .0002") on the end of the 12" Grizzly rod, and the indicator located very close to the breech (or muzzle as the case may be), he is measuring, being conservative, 1" and 3" from the indicator. The bushing will move more than the rod will at the indicator's location. But not much.
How much? would be a reasonable question at this point. Let's see if we can estimate it making reasonable assumptions.
In simple terms, neglecting the force of the indicator trying to bend the Grizzly rod, and the distortion (curvature) that obtains from bushing displacements on the order of 0.001" to 0.002" (they will be displacements more on the order of .0002 at the end of the centering process) at the end of a 12" rod, the movement at the indicator is 11/12 of the bushing movement when the bushing is at the breech end, and 9/12 of the bushing movement when the indicator is moved 2" into the bore as he says in the video. If one is using an indicator with a resolution of 0.000100" at the indicator tip, that says the real resolution is actually .000109" when the bushing is close to the breech and something like 0.000133" with the bushing pushed 2" into the bore.
Thinking about it, I'm not sure an indicator with a 2" tip is that accurate. Actually, if one puts a 2" tip on a 0.0001" indicator that originally had a 1" tip, the resolution is .0002", which is worse with out position and land jumping errors than the Grizzley rod.
But that may not matter. What one is doing is to locate the measurement point on the lathe spindle axis and have no movement at all, or as little as possible. I will be interested to see, but I think getting to that point is easier with out the "noise" of the tip bouncing over the lands.
I need to think about this a bit more, but I'd think if one dipped the bushing on the end of the Grizzley rod in oil before inserting it in the bore, it would provide a very nice smooth motion that would lend itself to easy interpretation. I.e. it would be easy to see when the motion stopped and was smooth. Slop could be eliminated as a source of error buy insuring there was a bit of tension in the rod by it being a tiny bit off center in the tail stock chuck so it would follow the ID of the bore on one side. The bore's deviation from round ought to be way less than the other errors or it isn't a very good bore.
It wouldn't pick up the variation in land height, but I wouldn't expect an indicator with a long tip will do that reliably either with all the bounding around.
I hadn't thought through that part of the process before. Interesting. I think it may be that Gordy's measurement method has less error than the long tip indicator, but I haven't tried it yet.
[/QUOTE]Gordy has a hypothesis, not a theory. Until it can be quantified through analysis of variance, or some other practical means, I would say he cannot correlate his increased amount of accurate rifles to the assumed angular alignment of the bore to chamber
Try this.....
Take a benchrest grade barrel and indicate it in the lathe 5 times using both methods. 10 times total. Remove the barrel from the lathe completely each time.
Check muzzle runout at the spider, and record it all 5 times using Gordy's methods. also mark the index point on the muzzle with a sharpie.
Let us know which method is more repeatable. Repeatability is the cornerstone of accuracy.
Ben[/QUOTE]
That's an interesting experiment. I may do exactly that. But the results may not tell you the same thing they tell me. What I may learn from the experiment is a way to do the measurement better, or at least to become better at using the instrumentation to achieve consistancy.
That said, just as we learn more from our failures than our successes, the most useful experiments are the ones that give an unexpected result.
We can agree to disagree on this, but to me, building on the instrumentation error discussion above, getting something exactly wrong in the same amount every time, while it is repeatable, is not the same thing as getting it approximately correct every time. In the latter case there is the opportunity for systematic improvement as tooling, instrumentation, and skill improve and the error reduces. In the former, there is only being even more precisely wrong by the same repeatable amount on a given barrel, with no opportunity to make it better than the average of the bores wandering around in the run of barrels chambered.
I'll probably use Gordy's approach, though I can understand why folks would choose to use the other. It has resulted in some pretty good barrels. There may not be much difference in outcome in some, or even most cases given the current available tools and instrumentation. But using Gordy's approach there is at least the chance for getting closer and closer to the best that a barrel/action/shooter can be as one's skill, instrumentation, and tooling improve with time and experience. That is not the case with the two point breech/muzzle approach. In any event, the difference in outcome is only knowable as a time average of barrel performance out of the same shop. And such an average may be really hard to track in any objective fashion. Gordy thinks that trend shows an improvement in his case.
For me, maybe not for everyone, I think trying to do my best with theoretically correct approach, within the limits of tooling and measurement errors, my skill level, and other considerations, will yield better results over time than doing as good a job as I could with an approach that basically averages the bore error regardless of measurement accuracy or perfection of implementation.
It will make me feel good, and that's worth something.
I see Gordy's approach as requiring a bit more skill, and the added task of managing the muzzle intercept, but I've got all day and nothing else to do, so I'll give it a go.
I do appreciate your taking the time to answer me. It was a good answer that stimulated the sort of dialog that promotes learning. (Dialog is a much more constructive form of communication than arguement IMO.) I learned something thinking through my reply. I have lot more to learn. But I think I'm gaining on it. I've spent decades working on a variety of problems where the right answer wasn't known, or even correctly guessed at, but had to be recognized when it showed up because we were betting the astronauts lives on the outcome, as it nearly always did.
I can't escape the though that Gordy's approach, because it's theoretical correctness holds out the chance for continued improvement, is on the right track.
Thanks
Fitch
Uh, yes, I think. I agree with what I think you intended to say.
In the name of precision (yes, language is a tough way to communicate
) I'd like the bullet path and bore to be coaxial vectors, the same, at the pont of entry (throat) and exit (muzzle). With that in mind, I could agree that the goal is to machine a chamber that is aligned with the bore axis at and for at least a bullet length beyond the start of the lands in the throat, and a muzzle crown the plane of which is orthogonal (at all points perpendicular) to the last bullet length of the bore axis at the muzzle.
That makes my head hurt, but I think it is correct.
I understand what you are saying, I'm not sure I agree with it in general but let me think for a minute ... OK ... lets do s thought experiment. Same barrel in both cases. The assumption is that the bore and the average centerline between throat radial location and muzzle radial location don't align where the chamber throat and crown will be located. I think we both agree that misalignment is more likely than not and only a matter of degree as a function of the barrel makers triumph over the variety of variables involved.
Suppose you can absolutely perfectly, with zero error, center the measured point at that selected location along the barrel in bore radially right on the spindle axis. If you do, you will still have the angular error between the spindle axis and the local bore axis that occurrs by chance. What ever reduction in group size occurrs as a result of the angular error can't be reduced even by unachievably perfect centering.
If, on the other hand, you could align the chamber centerline with the bore center line for a short distance, say a bullet length, past the throat, that will probably result in the most favorable bullet entry into the bore.
Your reply is based on our being able to do the first measurement more accurately than we can do the second, and for that reason the first measurement will result in the most accurate barrels averaged over time, and thus represents the best approach.
Could be. Can't rule it out with the data in hand, though Gordy thinks he has a different answer. See discussion after the next quote for more on this.
The down side to it is there is no chance to get better using the first approach. The best it can be will always be short of the best the barrel can be other than by chance.
Using the second approach, there is the chance to develop tools and instrumentation approaches that will result in improvement which will at least have the chance of improving shooting performance to what ever extent it can be improved by aligning things correctly. There is real appeal to following an approach that will respond to improvements as we get better.
That would be ~0.57 MOA if I did the math right.
You bring up an interesting point. I wonder about sources of error. Using Gordy's method, with fitted pilots (in increments of .0002") on the end of the 12" Grizzly rod, and the indicator located very close to the breech (or muzzle as the case may be), he is measuring, being conservative, 1" and 3" from the indicator. The bushing will move more than the rod will at the indicator's location. But not much.
How much? would be a reasonable question at this point. Let's see if we can estimate it making reasonable assumptions.
In simple terms, neglecting the force of the indicator trying to bend the Grizzly rod, and the distortion (curvature) that obtains from bushing displacements on the order of 0.001" to 0.002" (they will be displacements more on the order of .0002 at the end of the centering process) at the end of a 12" rod, the movement at the indicator is 11/12 of the bushing movement when the bushing is at the breech end, and 9/12 of the bushing movement when the indicator is moved 2" into the bore as he says in the video. If one is using an indicator with a resolution of 0.000100" at the indicator tip, that says the real resolution is actually .000109" when the bushing is close to the breech and something like 0.000133" with the bushing pushed 2" into the bore.
Thinking about it, I'm not sure an indicator with a 2" tip is that accurate. Actually, if one puts a 2" tip on a 0.0001" indicator that originally had a 1" tip, the resolution is .0002", which is worse with out position and land jumping errors than the Grizzley rod.
But that may not matter. What one is doing is to locate the measurement point on the lathe spindle axis and have no movement at all, or as little as possible. I will be interested to see, but I think getting to that point is easier with out the "noise" of the tip bouncing over the lands.
I need to think about this a bit more, but I'd think if one dipped the bushing on the end of the Grizzley rod in oil before inserting it in the bore, it would provide a very nice smooth motion that would lend itself to easy interpretation. I.e. it would be easy to see when the motion stopped and was smooth. Slop could be eliminated as a source of error buy insuring there was a bit of tension in the rod by it being a tiny bit off center in the tail stock chuck so it would follow the ID of the bore on one side. The bore's deviation from round ought to be way less than the other errors or it isn't a very good bore.
It wouldn't pick up the variation in land height, but I wouldn't expect an indicator with a long tip will do that reliably either with all the bounding around.
I hadn't thought through that part of the process before. Interesting. I think it may be that Gordy's measurement method has less error than the long tip indicator, but I haven't tried it yet.
[/QUOTE]Gordy has a hypothesis, not a theory. Until it can be quantified through analysis of variance, or some other practical means, I would say he cannot correlate his increased amount of accurate rifles to the assumed angular alignment of the bore to chamber
Try this.....
Take a benchrest grade barrel and indicate it in the lathe 5 times using both methods. 10 times total. Remove the barrel from the lathe completely each time.
Check muzzle runout at the spider, and record it all 5 times using Gordy's methods. also mark the index point on the muzzle with a sharpie.
Let us know which method is more repeatable. Repeatability is the cornerstone of accuracy.
Ben[/QUOTE]
That's an interesting experiment. I may do exactly that. But the results may not tell you the same thing they tell me. What I may learn from the experiment is a way to do the measurement better, or at least to become better at using the instrumentation to achieve consistancy.
That said, just as we learn more from our failures than our successes, the most useful experiments are the ones that give an unexpected result.
We can agree to disagree on this, but to me, building on the instrumentation error discussion above, getting something exactly wrong in the same amount every time, while it is repeatable, is not the same thing as getting it approximately correct every time. In the latter case there is the opportunity for systematic improvement as tooling, instrumentation, and skill improve and the error reduces. In the former, there is only being even more precisely wrong by the same repeatable amount on a given barrel, with no opportunity to make it better than the average of the bores wandering around in the run of barrels chambered.
I'll probably use Gordy's approach, though I can understand why folks would choose to use the other. It has resulted in some pretty good barrels. There may not be much difference in outcome in some, or even most cases given the current available tools and instrumentation. But using Gordy's approach there is at least the chance for getting closer and closer to the best that a barrel/action/shooter can be as one's skill, instrumentation, and tooling improve with time and experience. That is not the case with the two point breech/muzzle approach. In any event, the difference in outcome is only knowable as a time average of barrel performance out of the same shop. And such an average may be really hard to track in any objective fashion. Gordy thinks that trend shows an improvement in his case.
For me, maybe not for everyone, I think trying to do my best with theoretically correct approach, within the limits of tooling and measurement errors, my skill level, and other considerations, will yield better results over time than doing as good a job as I could with an approach that basically averages the bore error regardless of measurement accuracy or perfection of implementation.
It will make me feel good, and that's worth something.
I see Gordy's approach as requiring a bit more skill, and the added task of managing the muzzle intercept, but I've got all day and nothing else to do, so I'll give it a go.
I do appreciate your taking the time to answer me. It was a good answer that stimulated the sort of dialog that promotes learning. (Dialog is a much more constructive form of communication than arguement IMO.) I learned something thinking through my reply. I have lot more to learn. But I think I'm gaining on it. I've spent decades working on a variety of problems where the right answer wasn't known, or even correctly guessed at, but had to be recognized when it showed up because we were betting the astronauts lives on the outcome, as it nearly always did.
I can't escape the though that Gordy's approach, because it's theoretical correctness holds out the chance for continued improvement, is on the right track.
Thanks
Fitch
F
frwillia
Guest
No argument here.
The other stuff is sort of like what the guy said about why he climbed the mountain - because it is there. Why go in space? Because it is there. Why try to get closer to perfection (what ever that is) in chambering? Because we can.
Fitch