NEWS FROM THE TUNNEL, Barrel Indexing

[Stephen B Moore]

Jerry --

For only a small 100th of that amount I will part with my beloved '79 Triumph Bonny Special. It would look good on you. Mmmm, that was cash, wasn't it?
Steve Moore

 

[stiller]

Steve

Strictly harleys and harley aftermarkets. sorry NOW if you have a spare blonde, 30 to 50, hot with a good attitude that likes old fat guys.....

 

[Donald]

Very interesting Gene, and very simple too. I still think Vaughn's last idea of making a barrel thread and a means of fitting it tight to the action is the best. But that requires some extra machining on the barrel tenon, that as I remember had no threads at all. I will go check Vaughns book for the page number................. The pic is located on page 119 of the soft back version. And it gets tighter with temp. This would allow one to index the barrel any amount and keep the headspace the same. Cool thinking there. Course others will say if it ain't broke stop trying to fix it.
Donald

 

[mks]

That the shims you proppse would be a B word to make and a set screw is very simple. No doubt the shims would work but Why not go the easy route? If damaging the threads is a concern, use a Brass set screw.

Pete,
I like the shim idea because it would be less likely that the shims would compress and affect the indexing, versus it being fairly easy to cause a set screw to slip if some fraction of the 100 ft lbs of torque is applied to it. Slide the stack of shims onto the barrel tenon, torque the bushing onto the tenon at say 125 ft lbs, then screw this assembly into the action as if it were a one-piece barrel, and torque to 100 ft lbs.
I also would prefer not to disturb the symmetry of the action by drilling the set screw hole, particularly in the area of the barrel tenon. Vaughn talks about asymmetrical deformation in the action adding barrel vibration in unwanted directions. Maybe the set screw hole would have a small effect, but since it can be avoided, that's the way I would prefer. You might say that a set screw hole drilled through the vertical plane of symmetry of the action would only contribute vertical vibration, and you would be correct. But I would still rather not drill the hole.

Cheers,
Keith

 

[alinwa]

What you are saying means the bullet traveling down a curved barrel continues its flight in that curved path. It does not!!

??

Nope, that's not what I'm saying. What I'm saying is that for a given barrel indexing it your way "may" cause it to print 1/2 the distance closer to the bull than doing it the other way.

In other words, if you chambered a barrel Such that you've aligned the chamber and threads with the bore while "letting the muzzle flop" or run wild you may well have a rifle which prints its group lets say 8" over from another straighter tube........now, if you take it off and rechamber it your way you would now be grouping only 4" off center. No matter what you do with the curved bore it will still not be aligned.

No matter how you hang a banana it still doesn't point at the floor.

al

 

[JerrySharrett]

In other words, if you chambered a barrel Such that you've aligned the chamber and threads with the bore while "letting the muzzle flop" or run wild you may well have a rifle which prints its group lets say 8" over from another straighter tube........now, if you take it off and rechamber it your way you would now be grouping only 4" off center. No matter what you do with the curved bore it will still not be aligned.

No matter how you hang a banana it still doesn't point at the floor.

al

Al, you still don't get it, a curved barrel, regardless how curved does not impart a curve in the bullet path. What you are saying says it does and if so, indexing a barrel would only rotate the direction of that curve from horizontal to vertical. i.e. The rotation would only change the point of impact and that is why we have adjustable scopes, to move the POI.

However, the flopping barrel, pointing horizontal, does induce a variable side thrust to the assembly of the stock, action and barrel. This happens because the muzzle bore is now pointing in a different direction than the rest of the assembly. Rotating that barrel to vertical would reduce this effect. By properly aligning the chamber neck and muzzle bore before chambering would eliminated this problem to start with, even in an extremely curved bore.

Bananas have nothing at all to do with bullets!!

 

[stiller]

Just for thought,

but what makes ya'll think that the curve is in only one dimension. If the drill can wander up and down, it can surely wander left and right at times too.

 

[Gene Beggs]

Very interesting Gene, and very simple too. I still think Vaughn's last idea of making a barrel thread and a means of fitting it tight to the action is the best. But that requires some extra machining on the barrel tenon, that as I remember had no threads at all. I will go check Vaughns book for the page number................. The pic is located on page 119 of the soft back version. And it gets tighter with temp. This would allow one to index the barrel any amount and keep the headspace the same. Cool thinking there. Course others will say if it ain't broke stop trying to fix it.
Donald

Donald, thanks for the kind words, this has certainly been an interesting discussion.

It may very well be that Harold Vaughn had the best idea for a barrel receiver joint. I studied his version some years ago but never built one. I think it has a lot going for it. I'll try it and report my findings here on the forum. Thanks for reminding me about it.

Yes, there are those who are skeptical about barrel indexing but those who really understand the situation know there is great potential there.

You could take twenty new barrels, have the best gunsmith in the world install them without regard to indexing and you would be lucky to find one out of twenty that was competitive. One in twenty sounds suspiciously like the chances of one of those barrels being indexed exactly right, unbeknownst to the smith.

With a barrel indexing system, you can test the barrel in any position and find out where it shoots best. I test in hour and a half increments, i.e., 12:00, 1:30, 3:00 and so on but you could easily test in 15 minute increments; although, I do not think it is necessary.

I'm sure there have been many 'hummer' barrels discarded because they were not indexed properly. It might very well be that the worst bummer could be turned into a hummer by rotating a quarter turn on the receiver.

Later,

Gene Beggs

 

[Gene Beggs]

Al, you still don't get it, a curved barrel, regardless how curved does not impart a curve in the bullet path. What you are saying says it does and if so, indexing a barrel would only rotate the direction of that curve from horizontal to vertical. i.e. The rotation would only change the point of impact and that is why we have adjustable scopes, to move the POI.

However, the flopping barrel, pointing horizontal, does induce a variable side thrust to the assembly of the stock, action and barrel. This happens because the muzzle bore is now pointing in a different direction than the rest of the assembly. Rotating that barrel to vertical would reduce this effect. By properly aligning the chamber neck and muzzle bore before chambering would eliminated this problem to start with, even in an extremely curved bore.

Bananas have nothing at all to do with bullets!!

Jerry, I agree with Alinwa on this one. I think he has accurately described the situation and I think the banana analogy is right on.

Later,

Gene Beggs

 

[jackie schmidt]

Listen To Stiller

Any serious Machinist will tell you thata barrel's ID is not "curved", they are a product of the deephole drilling proccess where the gun drill might wander one way, and then a little ways up in, wander in another direction........jackie

 

[stiller]

Gene

explain how the curvature in the barrel effects the way the barrel vibrates and causes vertical versus horz. I will tell you now, there are at least 5 vibration modes in both vertical and horz that effect the bullet path. If you look at the frequencies of the first mode and at the velocity points that you come into tune, they dont correlate. It has to be a higher frequency mode. Maybe Varmint Al and his model will tell you which mode is the culprit, but it is not as simple as the barrel only moving in one direction and at one frequency and getting the bore curvature lined up.

 

[Gene Beggs]

Gene Calfee,
I think you have milked this enough. If you are going to tell us, go ahead. If not?
Butch

Mornin' Butch

Okay, if you're gonna' be that way; no more milkin', I promise.

BTW, how did you like the way I admitted Stiller was right? You can't be more direct than that; huh?

Later,

Gene Beggs

 

[Butch Lambert]

Gene,
If buddies can't rib each other, who can?
Butch

 

[Hal D.]

"You could take twenty new barrels, have the best gunsmith in the world install them without regard to indexing and you would be lucky to find one out of twenty that was competitive. One in twenty sounds suspiciously like the chances of one of those barrels being indexed exactly right, unbeknownst to the smith."

You are kidding, right Gene? 1 in 20? You honestly believe that a barrel HAS to be indexed in the vertical plane to be competitive?

 

[Big Al]

Good Lord, I love this stuff, it just doesn't get any better than this on any forum!

Please Lord, let this go on forever.

 

[JerrySharrett]

but what makes ya'll think that the curve is in only one dimension. If the drill can wander up and down, it can surely wander left and right at times too.

Jerry, I have preciously referred to barrel bores as wandering and they ALL do.

My point here thought is that a properly aligned barrel does not need to be indexed in the first place!!

Gene, you never did answer as to how this "needs indexing" barrel was aligned for chambering. And, I strongly disagree that only one in twenty barrels are Top-5 competitive. Tony keeps more than that and he is probably the most demanding shooter I know......except a certain shooter named Jack.

 

[Gene Beggs]

Gene,
If buddies can't rib each other, who can?
Butch

That's right Butch! I agree.

Come out when you can. Missed you at the Buffalo Shoot.

Later,

Gene Beggs

 

[Gene Beggs]

explain how the curvature in the barrel effects the way the barrel vibrates and causes vertical versus horz. I will tell you now, there are at least 5 vibration modes in both vertical and horz that effect the bullet path. If you look at the frequencies of the first mode and at the velocity points that you come into tune, they dont correlate. It has to be a higher frequency mode. Maybe Varmint Al and his model will tell you which mode is the culprit, but it is not as simple as the barrel only moving in one direction and at one frequency and getting the bore curvature lined up.

Jerry, I cannot explain in technical terms how and why a barrel vibrates, I only know it does and that this vibration is responsible for most of the inaccuracy in our target rifles. I cannot describe all the various modes of vibration and frankly don't care. As a shooter, I need only a basic understanding of barrel vibration and as long as I can turn my 4 ounce tuner no more than a half turn and always get the rifle perfectly in tune, that's all I need to know.

You are correct, barrels are not necessarily curved in only one direction. There may be several deviations throughout the length of the bore. I think this is the reason you cannot predict where the barrel should be indexed.

Now that we have a way to quickly and easily index the barrel without altering headspace, there is no need to determine where the curvature is. By test firing, we will soon find out where the barrel wants to be positioned and once this is accomplished, no further adjustment will be necessary.

Later,

Gene Beggs

 

[Gene Beggs]

"You could take twenty new barrels, have the best gunsmith in the world install them without regard to indexing and you would be lucky to find one out of twenty that was competitive. One in twenty sounds suspiciously like the chances of one of those barrels being indexed exactly right, unbeknownst to the smith."

You are kidding, right Gene? 1 in 20? You honestly believe that a barrel HAS to be indexed in the vertical plane to be competitive?

No Hal, I wasn't kidding. Maybe I should have said you would be lucky to find one "hummer" in twenty.

Hal, you asked, "You honestly believe a barrel HAS to be indexed in the vertical plane to be competitive?"

What part of the barrel are you referring to? We can never know until we shoot it what a barrel is going to do. There may be assymetries in the action that can be offset by a corresponding flaw in the barrel the result of which is to cancel each other out. With the barrel indexing system, we can now place the barrel in any position and see the results on the target.

Later,

Gene Beggs

 

[John Kielly]

I've always called myself a user, that is, I have great difficulty in digesting technical manuals, but can get a fair handle if somebody who can read 'em explains it in a way that I can understand.

Is what we're talking about here similar to the spine on a fishing rod blank? Tubular rod blanks inevitably end up with one point of the circumference being less homogeneous than the rest & that's that the point that you align the rings with or 180 degrees contrary to, depending if it's a plugcaster or whatever.

If you bind them on in another manner, the rod won't cast as well as it should & in some cases, the rings will sort of migrate the line towards the spine under load, causing the cast to go to one side.