Shadow line a bore

M

mshelton

Member
I'm not a gunsmith, machinist or even a guy that pokes around with it but I've seen that term in a couple articles and books as a method to determine the straightness of a bore.

I've tried to search on it and have seen some mention of it but for the life of me I cannot figure out what they are doing and how they go about it.

If someone would be kind enough to take a min or two and explain it to me in layman's terms, I'd really appreciate it, I'd really like to know what that processes is.
 
Without some means for a fixture, like a lathe, it's hard to describe. Suffice it to say that you look through the the id of the spinning barrel and you can detect quite small imperfections in how true the the inside of the barrel is as it spins.
 
I seem to remember a procedure that involved something that resembled a light table with alternating black and white stripes, mounted so that its surface was parallel with the wall that it was mounted on. By looking at it through a barrel, crookedness would be seen by the distortion of the reflections of the stripes. I have also heard of an old fashioned method that involved a bow with its string running through the the bore as a reference while looking through the bore at a light source. Beyond these, this may get you started in your search for information. https://www.google.com/search?q=methods+of+determining+rifle+barrel+straightness&ie=utf-8&oe=utf-8
 
Boyd Allen said:
I seem to remember a procedure that involved something that resembled a light table with alternating black and white stripes, mounted so that its surface was parallel with the wall that it was mounted on. By looking at it through a barrel, crookedness would be seen by the distortion of the reflections of the stripes. I have also heard of an old fashioned method that involved a bow with its string running through the the bore as a reference while looking through the bore at a light source. Beyond these, this may get you started in your search for information. https://www.google.com/search?q=methods+of+determining+rifle+barrel+straightness&ie=utf-8&oe=utf-8
Click to expand...

Never heard of that but it seems plausible. Heck, before you know it, we'll have experts indicating barrel throats by eye. ;)
 
mshelton said:
I'm not a gunsmith, machinist or even a guy that pokes around with it but I've seen that term in a couple articles and books as a method to determine the straightness of a bore.

I've tried to search on it and have seen some mention of it but for the life of me I cannot figure out what they are doing and how they go about it.

If someone would be kind enough to take a min or two and explain it to me in layman's terms, I'd really appreciate it, I'd really like to know what that processes is.
Click to expand...

It's looking through a rifle bore and seeing the curvature or lack thereof.

I can do it in a lathe. And I think I could do it in vee blocks, setting down...never tried.

Elmer Keith could do it by hand, well enough to get paid for it, as can some others.

I hesitate to call it an acquired skill and I'll go out on a limb to explain why. I'm a construction guy. And I can see flat, square, level and plumb as well as estimate lengths down to the inch better than anyone I know. This isn't bragging, just life as I live it. By the same token I've got some close friends and relatives that can run/feel/see/cut grades from the seat of a 'dozer better than a commercial laser-guided GPS'd grading machine....and they do it. Every day. They're in high demand. I have friends who can sculpt a hillside/homesite/driving area into an exquisite free-draining collection of angles and curves better than Monet can capture light and I know that I CANNOT......but I can sure see straight. Even from the side.

I routinely (did it for 5 hrs today, pouring footings) look around the jobsite and send men to fix things that they can't see. I got in an argument with a guy today regarding flat and we had to break out the lasers and strings and aluminum screeds to sort it out....And I work with guys who're very experienced, very good at their jobs and in many cases very aware that they don't possess this "gift." They're also aware that they can do/see things that I cannot in other areas. This is why I hesitate re "acquired skill." We do have different physical attributes.

BTST Elmer Keith could shoot a sixgun better than any fixture. As can Jerry Miculek.

(((Well, actually Jerry can perty much shoot ANYTHING better than anything else....but I digress ;) )))

Anyway, I can look down a rotating barrel and by moving my head over find a spot where a definite "shadow line" (or just shadows???? bores aren't just bananananana'd but sometimes twisted and other-woggled) flickers in the barrel. I don't use no steenking strings nor squares nor lines nor nuttin, just light, me. Nor do I claim to DO anything by it, just can see it.

sometimes.
 
If you take a barrel and aim it a a piece of white paper, you will see reflection circles form through the bore. If these circles appear oblong, the ID of the barrel is not straight with its self. If you see a succession of seemingly round circle reflextions, then the barrel Is reasonably straight.

Old master barrel straighteners use these circles in conjunction with a star wheel press to take minor kinks out of barrels. You watch the reflections as you apply pressure.

I know how to do it. But the kicker is, you will usually induce stress in the barrel.
 
Common practice used to involve using a string or wire stretched in front of a window. Looking through the bore at this would produce a definite shadow line which, if curved or broken, indicated a curve in the bore. This worked real well in a bore which was not yet rifled but rifling makes the line more difficult to read and using the concentric (or not) circles reflected in the bore seems to work better for me. There is a fairly good description of the technique in Ned Robert's "The Muzzleloading Caplock Rifle". Having read this book when I was young, I used this technique and it worked for me. I must confess, it worked much better when my eyes were much younger!
An early mentor had made up a barrel straightening press which consisted of a piece of I-beam with some blocks attached and a jackscrew in the middle. It worked reasonably well and I made myself one like it. Later, I used a hydraulic press and V blocks. Barrels straightened easily or with some difficulty depending upon the material. An old 22 barrel, for instance, was easy to straighten because the mild steel was relatively "dead" and had very little spring to it. A modern 4140 barrel was a different story and you had to bend it well past straight until it sprung back straight. You could feel when the barrel gave and you would then back off and see where you were. The whole thing is as much an art as a science and there seems to be a bit of a knack to it. Some are undoubtedly better at it than others.
One time I was visiting a barrelmaking shop and the owner was showing me some of their tooling. They had a nice old barrel straightening fixture with the star wheel as Jackie described. There were a bunch of blanks, which were drilled and reamed but not yet rifled, beside the press. I picked one up and looked through it and asked if they straightened the blanks prior to rifling. He replied, "Yes. Those have been straightened and are ready to be buttoned. Well, the bore I looked through looked like a sidewinder in a hurry so I commented, " I guess this one got into the wrong pile by mistake". He seemed offended.
There was a time when barrels were not always properly stress relieved and it was often necessary to straighten a barrel in the middle of the contouring operation. I recall one barrel which I straightened five or six times until I finally stuck it in the oven, which I turned all the way up, and cooked it for four hours then let it cool overnight. Surprisingly enough, this seemed to do the trick and it warped no more and no more straightening was necessary. This was a carbon manganese barrel and I don,t think this would have worked on a 4140 barrel (not enough heat). The point is (although I have certainly gone off on a bit of a tangent) I have straightened a bunch of barrels and have used a shadowline to gauge the amount of curvature. By the way, with the barrel spinning in the lathe, I believe I can see a couple thou of deflection and maybe less. If I find a barrel to be visibly straight, it is probably straight. Regards, Bill
 
Whether a barrel has zero bend or a slight curve has no effect on accuracy. The old barrel straightening method works ok, if, if, you are only going to shoot slow enough to NOT let the barrel change temperature.

In centerfire benchrest LV/HV/SP group we shoot usually 8 shots per target. In score the count is more than that according to the target.

When a barrel is mechanically straightened stresses are introduced. If hat barrel is now totally and entirely stress relieved, cryo or furnace, that barrel will crawl as it heats up...fact. And will mostly return to its initial state as it cools.

The worst curved barrel I ever had, really looked crooked spinning, inly had 0.013" of total bend.


.
 
While there can be no doubt that straightening or bending a barrel will induce stresses, there is some question as to just what the effect may be. Keep in mind, unless the barrel is stress relieved during the manufacturing process, the blank is likely to have stresses residing within anyway. Now, some people will say the material is received in a stress-relieved or normalized state but just because that's what the invoice says doesn't always make it so. I have worked with enough heat treated, stress relieved 4140, for instance to know each piece is likely to be unique.
To get back to barrels; I suspect that an attempt to straighten a select match barrel may well induce stresses, the effects of which might be visible in the BR arena. Given the context of a hunting rifle though, I have not seen a significant effect. One barrel blank was plainly not stress-relieved and the damn thing warped with every cut and had to be straightened, sometimes halfway through the cut. Nonetheless, it was eventually contoured and chambered for the 264 Win Mag and installed on a 98 Mauser. Concerned about all the straightening, I decided to test the barrel before bluing it. The barrelled action was screwed into an old mauser stock with no fore arm and then fed a whole box of factory loads over the course of about ten or fifteen minutes. It was some hot! The resultant group was about two inches at 100 and was round which no stringing in any direction. I have also straightened numerous barrels which had been bent in some mishap or another (horses, trucks, and ATV's often play a part) and always shoot them afterwards. Again, there has been no case of "walking" of the point of impact which could be attributed to this. Again, I'm not saying it doesn't happen; only, in my limited experience, it has not. Of course, I don't have the nerve to straighten a good shooting but crooked barrel to see if it gets worse. Call me chicken if you like. Cluck cluck. Regards, Bill.
 
jackie schmidt said:
If you take a barrel and aim it a a piece of white paper, you will see reflection circles form through the bore. If these circles appear oblong, the ID of the barrel is not straight with its self. If you see a succession of seemingly round circle reflextions, then the barrel Is reasonably straight.

Old master barrel straighteners use these circles in conjunction with a star wheel press to take minor kinks out of barrels. You watch the reflections as you apply pressure.

I know how to do it. But the kicker is, you will usually induce stress in the barrel.
Click to expand...

We do a similar thing. We have bushings that fit the bore and have a tiny hole. Held to a light rings are visible, concentric if the bore is straight and bunched to the side if not. Ones that don't pass the test are cut to become muzzle brakes.

Mark
 
Jackie Schmidt I was taught to do it exactly the same way you decribed it by a barrel maker and a dear friend. It also took sometime to aquire the skill but I was also fortunate to have him by my side while learning exactly what to look for as he would continualy point it out while we were both looking down the same barrel. Also the more one does it the easier it becomes for one to more clearly see.

JLouis
 
So, what is the process

once one sees where the crook or bend is, how is the barrel marked so that it can be straightened, if that is the intent? What if a person were to not bend it exactly where the crook is? Seems like a lot is left to the "Feel" of the whole process.

There has been a thread on the Air Gun forum about this subject and it was generally agreed on that straight barrels yield better, tighter groups. It appears some manufacturers of Air Guns do straighten their barrels.

On that thread, I brought up the subject of heat straightening. I have seen some Youtubes of guys heat straightening various items such as long propeller shafts and tool arbors. One would think that the same techniques could be applied to rifle barrels, no?

Pete
 
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