NEWS FROM THE TUNNEL, Barrel Indexing

Think of a slotted screw being tightened till it bottoms. The final orientation of the slot after tightening depends on where it picks up the first thread of the threaded hole. If the hole itself is rotated then the final position of the slot, relative to the viewer, will be rotated by a similar amount. Screw a slotted screw all the way into a nut. now turn the nut. The slot rotates with it.
Obviously we will not be rotating the receiver, but if we make an inside and outside threaded bushing to fit the receiver threads, that is shorter than the action threads , there as range within which it can be adjusted without running into the back of the action threads or past the face of the action. As this bushing is screwed in and out within this adjustment range, the starting point of its internal thread is moved by the same degree of rotation. Like the slot in the screw the indexing of the barrel is changed ...by turning the "nut" or in this case the threaded bushing.

IMHO the difference or similarity in thread pitches is irrelevant, since we are stuck with the action thread pitch, and it is the determining factor as to how far the sleeve will have to be turned in or out to cause the start of the internal thread to make a complete 360, The barrel will effectively index with the start of the internal thread. The internal thread pitch only determines the thread depth, strength, fit requirements, and rate of barrel advancement while tightening. Jerry..Gene....Al?
 
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Gene, I have it... no action mods!

With your system, there is a gap between the outboard end of the bushing and the barrel shoulder that will vary as the bushing is rotated in the action threads, but if you install the bushing on the barrel tenon first ,with different thicknesses of shims to fill that gap (depending on where you want the bushing's OD thread to be indexed relative to the barrel), and tighten it in place against the shoulder(slot of back end?), you will have what you need without modifying the action. The worst that can happen is that you will leave the bushing in the action when removing the barrel, and by leaving the slot in the outboard end of the bushing, you will have the needed purchase to remove it, with a tool.
 
alinwa said:
Nope.... :eek: turns out I'm lost. I hadn't thought it through yet. I'll back off and draw pictures now.....:eek:

al
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Wellllll, I thunk on it. I pictured it. And I now have to agree with Stiller :D

THE ONLY WAY to quickly change the location of the ramping surface in relation to the action face (headspacing surface) is with dissimilar threads. I have a hunch that same-pitch threads would work due to diametric difference but only over a long run of threads. Basically, when the interior and exterior threads ar the same pitch they very nearly "follow each other" without effectively changing the bottoming surface.


Steenking Stiller :cool::cool::cool::cool:


LOL


al
 
Boyd, Boyd Boyd

we send ya to school, ah you know the story. THINK it through. Analyze how far the sleeve moves out with a 1 turn out and how far the barrel moves in with that same 1 turn. If the TPI is the same the amount it moves per turn is the same and the barrel does not end up at a different rotational spot. This is a simple problem.
 
Hey Boyd,

Think of it this way.....

Picture if you will setting the barrel index right where you want it and then tightening the "locking ring" (the threaded bushing) from the back side. Impossible I know but PICTURE it ;) you run your spanner up into the gap from the BACK side and engage your notches. Now, if you had matching thread pitches you could just screw your threaded bushing back and forth freely, no tightening effect.........


hth???




IMO a tighter pitch on the outside of the bushing is efficacious as a simple rotating fit with NO THREADS would be very direct, 1/1. You want the bushing to move longitudinally as little as possible.


al
 
Jerry...my man

I got half way through an eloquent dismissal of your point...when I got it. Oh well, it turns out that engineers are good for something after all. I still think my idea about assembling the sleeve to the tenon, tightened against a shim specific to the barrel index desired would work, and eliminate the need for drilling and tapping a hole in the action. Thanks for the lesson. I guess this means that I should tear up my application to Mensa.;)
 
ZDH said:
Gene, with this new system you have come up with, is there still a need for a tuner?

Oh, by the way, I finally installed the tuner I ordered from you several months back. I will call you next week to get your expertise on adjustments.

Thanks,
Zach
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Zach, this barrel indexing system is not associated with conventional muzzle tuners. Indexing is a one time thing to determine the exact position at which an individual barrel shoots best. A punch mark or scribed line can be placed on the tenon to identify this position should the barrel be removed for any reason. The tuner, on the other hand must be adjusted quite often to compensate for changes in atmospheric conditions.

Later,

Gene Beggs
 
jackie schmidt said:
Have you ever stopped to think that all of this effort is based on a false premis that you mistakedy stated as fact in your unitial post??..........jackie
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Jackie, I'm sorry but I don't follow you. Please explain. What did I state in my initial post that you believe is a false premise?

Gene Beggs
 
Boyd Allen said:
With your system, there is a gap between the outboard end of the bushing and the barrel shoulder that will vary as the bushing is rotated in the action threads, but if you install the bushing on the barrel tenon first ,with different thicknesses of shims to fill that gap (depending on where you want the bushing's OD thread to be indexed relative to the barrel), and tighten it in place against the shoulder(slot of back end?), you will have what you need without modifying the action. The worst that can happen is that you will leave the bushing in the action when removing the barrel, and by leaving the slot in the outboard end of the bushing, you will have the needed purchase to remove it, with a tool.
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Boyd, this was considered but ruled out because it is much easier to simply lock the bushing in place with a set screw. No shims to keep up with.

As far as modifying the action is concerned, I do not consider putting a set screw in a hole that is already there a significant modification.

Later

Gene Beggs
 
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Hi Gene, this topic was discussed in depth awhile back, although.......

...............buried in a long thread on perhaps the long range or gunsmith forum, about installing a single barrel into different thread pitch style actions and achieving different barrel orientations.

Differential threaded insert was the consensus solution of this particular discussion, although using a spannar lock ring (Savage style) to secure the assembly.

Jerry Stiller is correct, the thread pitch needs to be different from insert vs. barrel..............maybe Gene created enough of a variation in cutting the various internal/external threads of the insert vs. the barrel tennon thread pitch to accomplish differential indexing.

Rough calculations were done to estimate the pressure vessel strength of one piece tennon chamber vs. a smaller diameter tennon with differential insert thread, resulting in same overall diameter, by perhaps Jerry Stiller or Vibe, and the consensus was that there was probably less than a 10 percent loss in vessel strength.

Major concern of part of the past discussion was the material used to make the differential threaded insert or spannar nut.............many felt it was a big mistake to use the same material for insert, spannar nut, as the material used for the barrel (416 stainless) due the probability of galling due to material similarity.....................Don
 
Gene already said...

Gene already said the outside thread are 18tpi & the inside 28tpi. With those threads, it would only take 64% of a turn of the sleeve to give a complete turn of the barrel.

My question is how did he keep the set screw from buggering the threads? Plastic or brass tip? Ball of lead under the set screw?

If the sleeve were split, then the set screw could tighten up both the sleeve & barrel from turning.

Regards, Ron
 
Good morning guys. The feedback reveals that we have some real thinkers following this thread.

After carefully studying the posts of Jerry Stiller, Alinwa, Boyd Allen, Jackie Schmidt, Don Jackson and others, I am still not convinced that you cannot use the same threads on both the bushing and barrel tenon. Obviously, there is only one way to find out for sure and that is to make one and try it. I'm headed to the shop.

Later,

Gene Beggs
 
A question about Indexing - - -

Can the index point of a barrel be determined before it is finally fit to an action or does it need to be fitted to show where the 12 o'clock position needs to be? I have read other posts in which barrel indexing was lightly discussed. I am thinking the 6:00 point or the "Droop" of the muzzle, if you will, was positioned at 12:00. Is the bushing method an improvement over this method?

Thanks, Pete
 
Gene,
After some thought, I believe that Jerry is right.

Try looking at it this way, If we installed a bushing with the same internal and external thread pitches, that extended past the front of the action, and had a provision so that it could be turned, and screwed in a barrel with no shoulder, and extended threads, we could (with a loose fit and lubrication) hold both the action and the barrel in vises (bolted to a common surface)and turn the sleeve, since the identical internal and external pitches would advance at the same rate. Having the barrel clamped would impose the same limit as its having a shoulder that was tightened to the action. As the bushing was rotated, there would be no pull or push on the barrel relative to the action.

Looking at it another way, with the same pitch inside and out, turning the bushing in would give the same effect as back boring the action thread with no bushing. There would be no effect on the indexing of the barrel.
 
I like it Gene, very simple. If you thread the insert home to the shoulder on the barrel using a 4pt notch wrench, you would have no need for a set screw. Using shims now would make your install easy. A shim placed in front of the insert would start the clock at a different position. Tightening the barrel on the action will likely tighten this sleeve further so make sure you can get it off.
 
Gene,
It was implied that , all that was needed was an action wrench
and barrel vise.
A bushing with similiar threads in and out would advance at the same
rate. Moving the bushing would have no more affect than removing
the first thread .0138( 1/4 turn) back . The shoulder still stops at the same
place. Another 1/4 turn deeper, and the only thing that has changed
is the position of the bushing. The stop point is the same.
A set screw can impose an axial force on the bushing , much the same
as a sight base screw which is to long can on a barrel tenon. I would
think a set of spacers would be much better
 
Gene, Jerry-

Is correct. The internal & external threads have to be different. Picture the bushing with the same pitch threads in the action, locked with a set screw. [sight base screws have really locked a bbl. in the past] If the bbl. clocks up at 9 o'clock, you remove the bbl., adjust the bushing in or out, the bbl. is not smart enough to know the difference. It will clock up at 9 o'clock whether A.M. or P.M.
If you have 18 tpi =.0555" gain or loss per revolution, it does'n change inside versus outside.
If you make the bushing 18 tpi od and 28tpi id, bbl. tenon threaded 28 tpi =.0357" , screw the bushing in the action, lock it in place, screw the bbl. in. If the bbl. clocks at 3 o'clock, remove the bbl., unlock the bushing, move the bushing IN 1/4 turn =.0138". Should put index mark right at 12 o'clock. If the bbl. indexed at 9 o'clock to start with, screw the bushing OUT 1/4 turn = .0138", bbl. should now index at "High Noon".
Each "hour" of the clock is valued @ .0046".

There are probably 4 Moore pages of wills and wont work posted by time I got this typed.

"Timing IS Everything" Steve Moore
 
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