Dialing in your bbl

B

bob3700

Member
Here we go again. The more I do this the less I know.

For an open discussion, I was watching Gordie Gritters use his indicating rod method of dialing in a bbl. His goal, it would seem, is to get two inches of the bbl bore to indicate true to the center line of the lathe. That makes sense to do.

Being a HP shooter, I use a front sight that is mounted via a bbl band. To have the muzzle of my bbl true for two inches and then turn the outside of the bbl for the sight mount band run true to the bore sounds good to me. Have the bore straight where my sight is looking.

Using Gordie's method of working thru the headstock (it is the method I use anyway), he uses the chuck and spider to adjust the bore to run true for two inches. I did that. It takes some work to refine your technique, but finally I have the bore running under .0005" for that distance.

Now here is what causes me to ask your thoughts/opinions. I looked at the breech end of the bbl running in that spider, and it was making some pretty good sized elliptical circles back there.

So what the ZZZZ? Are you actually inducing (bending) the bbl to get the bore straight for that two inches you are indicating off of?

It would seem that no matter where you indicate, the bores of these fine SS Match grade wunder sticks, they are not very straight for very long. It would seem that indicating at a specific point is OK but you are not guaranteed of any straight section immediately in front of that point.

Any more, I am becoming very skeptical when people are indicating their bbls in to .0002" cause that is lost in the next .050" down the bore.

Me thinks there is a lot of fly ShxT in this pepper we call chambering.

Bob
 
Let me say that I am not a match shooting champ or any thing like that.
But I have spent some time trying to think like a bullet.
I think there are two critical time windows, in a bullets path down the bore.

The first window, is that first bullet length of travel as it exits the case and enters the bore/lands. Hopefully it should be as in line with that 1 or 2 inches as possible, so that there is no unwanted deformation.

The second window is it's departure from the muzzle.
In a perfect world the first inch or two and the last inch or two
would be in alignment axially and concentricly. But that ain,t likely to happen.
Drill bits are going to wander.
Thats the way I see it. There is another thread on this same situation a little farther down the line. I think an exagerated drawing might be in order to clarify things.

Aloha, Les

Ain't a horse that can't be rode,
Nor a man that can't be throwed!
 
Bob, I think for your sights to work, you need to indicate both ends. Barrels aren't perfect so no chamber job can be perfect. If you indicate the throat and the crown, then drill and taper bore to the throat, your chamber will be true and coaxial to the lathe bearings at the throat. How far off would a crooked barrel be for another .250-.500 down the barrel? No more than the one chambered with a rangerod and your muzzle will be aimed in the right direction.
Butch
 
Gordie's method uses an indicating rod to get the barrel aligned but he always removes the rod and uses a long reach indicator, reading directing on the barrel grooves before reaming the chamber or cutting the crown. Using the rod initially decreases setup time and allows you to easily run the bushed rod in and out of the barrel to see how much crook you are dealing within a inch or two of the lead or crown. I've found very little adjustment is needed when direct checked with a 2.75" reach Interapid before cutting.
 
Roger, I guess that he has changed his method since his movie then. What indicator does he use with a 2.75 probe and in what graduations?
Butch
 
Roger,

Running the indicator in for a final dial-in is fine. My point was that to get that muzzle or breech to run true for two inches, you are working the bbl with the spider. Once that end of the bbl is dialed in for the two inches, the opposite end of the bbl is not running true. It is running is a pretty large elipse.

Somehow that just doesn't seem like it will produce a good outcome for muzzle or chamber.

It would seem that dialing the bore at the muzzle and throat to be the same would achieve the desired result. Better accuracy.

Bob
 
One of the most respected Benchrest gunsmiths dials his barrels in at both ends (through the headstock). Evidently there is more than one way to skin a cat.
 
I've been too busy setting up my "new to me" Harrison M300 lathe to reply.

Butch if I remember correctly the long indicator was a Interapid .0005", the others were various Mitutoyo, etc., .0001". The video doesn't show everything but I know he teaches to recheck the run out several times during the machining process, ie after threading, boring, before final reaming etc and it's alway direct read, down in the barrel on the grooves.

Bob,
What you are saying is true, if the bore isn't perfectly straight there will be a curve or spiral in the middle. It takes a bit more time to set up both end to be true but that is where the bullets starts and exits, not much we can adjust down the middle of the run. You do have to momentarily loosen two screws in the spider and chuck, 90 degrees from each other to insure that you are not imposing a bending force on the barrel when dialing both ends to run true.
 
Fella's,

Well, I can tell you my results turned out pretty good.

I dialed the breech end of the bbl in using my range rod and snug bushing. I put the bushing into the bbl the distance where the throat of the chamber would be (measured this off a loaded round) and indicated down into the tenths on this.

I dialed in the muzzle end (with deltronics pin installed) to less than 1 thou.

Now I do beleive that in order to maintain this precise set-up you have to take small cuts for your tenion turning and threading (my machine is a 13x40 Jet). After each operation, I again checked the throat for alignment.

Once the chambering was complete, the throat had runout in the low tenths and the chamber matched the same runout. I was pretty pleased with this.

I did get a chance to use the Lambert/Kiff micro-stop on my reamer. Boy, what a sweet tool. It makes that final reaming for headspace child's play. I hand reamed the last .010" by hand and got the bolt to close with just a hint of friction on the go gauge. What a great tool.

I feel pretty confident that I have found a fast and accurate way to dial my bbls in now.

Thanks to everyone for their input.

RGDS

Bob
 
Butch Lambert said:
Bob, I think for your sights to work, you need to indicate both ends. Barrels aren't perfect so no chamber job can be perfect. If you indicate the throat and the crown, then drill and taper bore to the throat, your chamber will be true and coaxial to the lathe bearings at the throat. How far off would a crooked barrel be for another .250-.500 down the barrel? No more than the one chambered with a rangerod and your muzzle will be aimed in the right direction.
Butch
Click to expand...

I'll offer a different hypothesis:

The bullet always, every single time, leaves the barrel going in the direction the last half inch to inch of the bore is pointing (I doubt that the bore changes direction very much in the last inch). This initial direction is modified by the effect of any assymetical gas pressure that will happen if the plane of the crown isn't perfectly orthogonal to the centerline of the bore for the last half inch or so at the muzzle, and the effect on the flight path of any deformation or skewing of the bullet imposed by a less they symmetrical entry into the lands.

The sights will work best if the critical bore segment at the muzzle, discussed above, is aligned so that the bullet flies in a vertical plane that is aligned with the receiver centerline in windless conditions.

With that bit of physics as a basis, the way to get the sights to work (or the scope to be aligned with the bullet path in windage) is to chamber the rifle so that the barrel is tightened into the receiver and properly headspaced with the that critical part of the bore pointing up in a vertical plane that is aligned parallel with the receiver centerline. The crown must, of course, be machined so that the plane of the crown is at all points perpendicular to that bore segment, and that won't happen except by coincidence when it is aligned by centering the bore at the breech and muzzle.

Aligning the breech and muzzle aligns nothing in the bore with the lathe spindle axis other than by coincidence. If a lot of barrels are considered, aligning the breech and muzzle results in an average misalignment that is less than would happen with out doing that, but it has no chance of being perfect other than by coincidence. The only technique that allows for improvement beyond coincidence is to measure the direction of the bore centerline at the muzzle and control where it is pointed during the chambering process. This latter approach is what Gordy's method accomplishes at the muzzle.

That said, I don't think anybody has compiled data that would demonstrate quantatively how big the difference is. With out that data, the process of choice would seem to be the one that accounts for the bore orientation and manages it rather than just averaging the misalignment and hoping for the best.

The theoretical benefit of Gordy's method is that the directionality of the bullet path relative to the receiver centerline isn't dependent on the the luck of the draw when the barrel maker picks a barrel to send the gunsmith, it is specifically controlled to within machining tolerances by the barrel chambering and fitting process. For purposes of sight performance, the angle at which it points up into the vertical plane isn't nearly as important as having that vertical plane aligned with the receiver centerline.

It occurrs to me that it might be interesting to align the barrel, breech and muzzle in the headstock as described, then put a laser bore sighter in the barrel on a near perfectly fitting mandrel that is aligned with the last half inch or so of the bore, project it on a wall or a piece of paper some distance away and see how big a circle it makes as the lathe spincle is rotated. This experiment conducted over several barrels might result in some useful data. The projection distance for measurment might have to be 25 to 50 yards for some barrels, less for others.

Fitch
 
Fitch,
I think you have said a whole bunch of words that doesn't mean a lot to me. I say that the iron or glass sights will be off a greater amount doing it Gordy's way. I think that it would be very hard to find a elipse or curve in a barrel. I would believe a helix is more probable.
Why don't you get a few barrels and prove what you are talking about? Unless you are lucky, chambering with a range rod and disregarding the muzzle until after chambering, will have the barrel printing a long way off.
Butch
 
Agree with Butch..

Butch is right. I have seen factory guns that the front and rear sights had to be off set to align with the bore. I have seen factory guns that the sights did not have enough adjustment (vertical) when the bore was out of alignment and finished turned up. However I don't think with high quality barrels this is as much of an issue with scoped rifles because the misalignment is very small.

Rustystud
 
Before everyone got quite so hung up on dialing in with the barrel through the headstock, it was common procedure to thread the barrel between centers. If the centers were cut true to the bore, thread alignment would be nearly perfectly co-axial with a line running from breech to muzzle. The actual bore, of course was likely to have a certain amount of curvature. The barrel was then mounted in the four jaw chuck or the steady rest for chambering. In general this worked out just fine and still does. If the barrel was too crooked, there could be a problem getting the chamber aligned with the bore and, if it was, it wouldn't be aligned with the threads. Truth is, if the barrel was that bad, it was no damn good anyway!
I like to align the threads with the "average" boreline and align the chamber with the breech end. With good barrels, they are pretty close to the same thing.
I have a mid-seventies Hart barrel which, when it is spun in the lathe, looks perfectly straight. That barrel was a real treat to set up and chamber. If a barrel looks like a skip rope, it probably won't be a BR barrel anyway but will make a fine elk gun. Anymore, If i'm planning on making a precision rifle and if the barrel looks too crooked, I'll just send it back and get another. Life's too short to struggle with bent barrels when straight one's are available. Regards, Bill.
 
Bill Leeper said:
Before everyone got quite so hung up on dialing in with the barrel through the headstock, it was common procedure to thread the barrel between centers.......... In general this worked out just fine and still does.....

Anymore, If i'm planning on making a precision rifle and if the barrel looks too crooked, I'll just send it back and get another. Life's too short to struggle with bent barrels when straight one's are available. Regards, Bill.
Click to expand...

Bill,
I mostly agree with what you are saying but I think you make the case for a better way of aligning. Isn't that why most (or many) 'smiths prefer to chamber through the headstock? To allow you to cut the neck straight with the lead, in a barrel that is not straight.

As for as sending barrels back again I agree but where do you draw the line? If you slug a new blank does it have to be perfect, one tight spot, two? Same with bore run out, all makers know that some have it, can't send too many back.

I think most folks here think point blank, 6ppc with 22" finished barrels out of a 27" or longer blank. If you work with long range barrels finished ~30" it's more difficult to move to and cut at a better part of the barrel. Same on long cartridges, a short range shooter I know just runs a finish reamer in the back of the blank, cuts the entire chamber after indicating off what will be cut for the cone and is happy. Obviously that works for him but if you chamber a long magnum that way the run out at the lead stands a much better chance of running out(!). I wonder about long VLD bullets compared to stubby short range bullets, just as a short range shooter cares little about SD and ES on the chrono but long range has to watch and weigh, different influence. I'm old enough to know a lot but don't, just trying to learn a bit at a time...... If we can find ways to minimize the variables, that's a good thing?
 
To Each His Own

Greetings,
I have watched the Gordy Gritters Video several times. The indicator is a Mitutoyo .0001 test indicator with the longer 1.5 inch pointer installed instead of the .700 length pointer this makes the variation twice what it shows on the indicator and it is used only to check the run out.
Try as I might I can not see how you can have both ends of a barrel running true with out bending it. I can envision that there are two points along the bore one on each end of the middle that you could cut the barrel and have both ends running true. When you look at the tolerances of deep hole drilling and what that deep drilled hole looks like in cross section you will see what I mean.
Jackie gets both ends running true so that he can have repeatability on his set up when he sets back his barrels, an event that he performs regularly. I have the utmost respect for Jackie and his reputation speaks well for his methods. I just can’t figure out how he makes this happen with out bending the barrel.
There are many ways to skin a cat, what is important is that the cat is skinned and skinned well. That is, the chamber is cut so that there is no run out and it is aligned perfectly with the bore in the throat and the barrel shank and thus the receiver. I use a method that is sort of a hybrid between the Gordy and Greg methods, which is I use both to check each other. I have little concern about the muzzle end until it’s time to cut the crown and I turn the barrel around in the lathe. I very rarely set back my own barrels let alone one for a customer, it is not cost effective. However I do not shoot a 6 PPC, I shoot a 30X47 HBR and a full .308 Winchester, these cartridges are easy on a barrel.

To Each His Own,
Nic.
 
Roger,
Most BR gunsmiths do prefer to chamber throught he headstock and, generally speaking, it's a good system. I also think it's a fine idea to try and have the first portion of the barrel aligned with the chamber. All of this is easily done if the barrel is reasonably straight and true. If it isn't, things don't work out so easily.
If I'm working on a BR rifle, or any kind of match rifle, that barrel better not have any tight spots. If I want barrels with tight spots, I wouldn't have to buy a select match grade barrel. I figure, if i'm spending money on a premium, hand lapped barrel, I surely shouldn't have to lap it again. I should not be able to do as well as the guy lapping the barrel in the maker's shop.
The same goes with bore runout. Some runout is unavoidable but, if it's excessive to the point that it makes chambering a challenge, the barrel is no good as a match barrel IMO. It's probably just fine as a hunting rifle barrel but it costs money to chamber crooked barrels if one wants to do the best possible job of it. I have seen barrels which, if the chamber portion was set up to run true for the length of the chamber, the muzzle end would show a TIR of 1 inch or more! Try and sight that baby in! Regards, Bill
 
Niccolo said:
Greetings,
I have watched the Gordy Gritters Video several times. .

To Each His Own,
Nic.
Click to expand...
Nic, remember your plane geometry. Two points define a straight line....any two points. So, pick a point where the chamber neck/leade center coincides with the barrel bore center and a point where the center of the muzzle is. Line up these two points along the line that is the centerline of your lathe spindle and, BINGO!

There is really nothing you can do about any barrel bore center points between those two that are not on that line.
 
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