NEWS FROM THE TUNNEL, Barrel Indexing

My first Br gun was a 222 40xbbr with a long barrel. Walnut stock
.250 neck and all. It turned out to be a straight shooter. As a matter
of fact, I spent 2 days shooting it next to Pat McMillian where
he shot a .16 agg and was the winner. He told me that was the best
shooting 222 he had ever seen. I thought it should shoot around
corners as the barrel had one hell of a curve to the bore from
10 oclock to 4. I wore it out.
Now I'm playing with a 6br that will shoot Vert with 4198 and
Horizontal with everthing else. It is a lite barrel(very lite in fact)
with what seems to be a definite choke at the muzzle.
Go figure
Now if temperature is the key to tuning/ because its an easy way
of following relative humidity, then why is humidity not also
important.
I find it strange that in phoenix, people shooting in the
Arizona heat went down with powder and people in Tex.
shoot 30 plus in that heat. What is the difference??
I must tell you that I have a shilen barrel that is deligted
with 26 gr of 4198 from april thru july and august and was
still piwheeling X's this sunday.
 
stiller said:
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.
Click to expand...

Jerry,
If you look at the zoomed graph of the ladder test on VarmitAl's Esten tuner page and estimate the time from peak to peak of the dominant vibrations that are being tuned, you get about 87 kHz. Definitely a higher mode. The 50 fps sweet spot shown in the graph agrees pretty well with those who say they have a window about the same range with their tuner.

Cheers,
Keith
 
stiller said:
it is not as simple as the barrel only moving in one direction and at one frequency and getting the bore curvature lined up.
Click to expand...

Exactly. The strategy is to force all of the motion to occur in the vertical plane, and then tune it to our advantage. This means indexing the barrel so that its major curvature is in the vertical plane, and hoping that very little is left in the horizontal. But it also means minimizing asymmetries in the rest of the rifle side to side. Traditional actions have a huge asymmetry with a port on one side. Left and right dual ports could be made exactly the same to maintain symmetry. Gas ports should be symmetrical too. Some BR actions have long, heavy bolt handles, which may be the greatest single source of horizontal asymmetry on those rifles. How about using dual handles of exactly the same size and weight, or at least reducing the single handle (light carbon fiber)? Scopes with big knobs on one side also cause asymmetry... Just some ideas...

Cheers,
Keith
 
If I'm reading this correctly, Gene is trying to use basically a "Twinsert" to do barrel indexing? Correct?

Something similar to the method used by Ken Markle to do neck turner cutter setup.

In a conventional action as is used for most PPC's (Short range BR guns), isn't wall thickness going to become a consideration? 4 thread pitch heights, plus enough material to keep the twinsert together, seems like a lot of material off the barrel tenon. For a barrel-hanger gun, this seems like it might defeat it's own purpose. Just a thought.

This also seems like it would be a difficult part to make.
 
Gene
How about putting a 2 to 1 ratio on your bushing? 16 thread action 32 thread for the barrel. Move bushing a 45 degree for every 90 degree you want to change the barrel. Bushing .0078 out (45º) and barrel .0078 in.(90º)

Glenn
 
Gene...

Here's a couple of ideas you might consider. The one with pins has about 25% less area in shear than the double threaded arrangement. Unless you really tighten the barrel in the receiver this should be ok.
Stress in the shank would be approx. 1.6 times the internal pressure in the chamber, that is if you had 50000 case pressure then the hoop stress in the shank would be about 80000 psi.
If you went with the double thread arrangement you do need to have different pitch in the threads. What's shown is 16 tpi in receiver and 20 tpi on the shank.
What's shown is .420 case diameter. If you went with 222 case diameter then you have lower hoop stress in shank.
 

Attachments

  • 100-0001_img.jpg
    100-0001_img.jpg
    37.2 KB · Views: 489
  • 100-0003_img.jpg
    100-0003_img.jpg
    31 KB · Views: 446
Last edited:
An answer to this problem could be a sleeve with a thread matching the barrel shank (presumeably right hand thread) and threaded with a left hand thread of the same pitch (threads per inch) on the outside. (With a matching LH thread inside the action). The sleeve would need a Hex Head and locking nut. As the barrel is rotated the sleeve would have to be rotated in the opposite direction...exactly the same amount. This would maintain headspace and allow rotation of the barrel relative to the action BUT whether it would be a practical set up on the range I am not sure. Herbit ...New Zealand
 
sorry mate

but wouldnt 1 left 1 right same pitch be the same place.cant see how it would work.Jerry is the man.:D
 
We've had this conversation before..quoting Jackie and myself

JerrySharrett said:
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.
Click to expand...

Look especially at posts #20, #23 and #34

http://www.benchrest.com/forums/showthread.php?t=48746&highlight=wandering
 
Herbit said:
An answer to this problem could be a sleeve with a thread matching the barrel shank (presumeably right hand thread) and threaded with a left hand thread of the same pitch (threads per inch) on the outside. (With a matching LH thread inside the action). The sleeve would need a Hex Head and locking nut. As the barrel is rotated the sleeve would have to be rotated in the opposite direction...exactly the same amount. This would maintain headspace and allow rotation of the barrel relative to the action BUT whether it would be a practical set up on the range I am not sure. Herbit ...New Zealand
Click to expand...

Could this be a simple threaded adaptor, with a right hand outside thread, left hand inside thread, and a left hand barrel tenon?
Click to expand...

As far as holding the bushing, it would be a slight tight fit on the barrel tenon, rotatable with a wrench, perhaps pliars. Being the threads would counter each other, there would not be a great urge for the bushing to rotate while tightening.
Click to expand...

I think the LH/RH scenerio might work. If it did, it might not require anything but the bushing. The concern would be; no slippage of the bushing while torqueing, and the holding integrity of the made up thread, after torqueing.

I am not saying clocking is necessary, and am not crazy about a bushing being located here.

I think it is worthy of consideration. And it seemed to fit the model of the exercise being proposed.

/\ \/ bushing
/\ \/
/\ \/ inside LH tenon threads, outside RH receiver threads
/\ \/ inside threads tight on barrel tenon, movable with suitable wrench
/\ \/
____recoil lug or barrel shoulder


Turning the bushing on tenon changes barrel clock position.


longshooter
 
Last edited:
Are CF barrels indexed by top gunsmiths?

I know that there has been quite a lot of indexing activity in rimfire rifles. Some of these actions had clamped-in or pinned barrels, along with a type of reverse cone extraction groove.

My question is, " How many of our top gunsmiths have experimented with indexing and what results did they get?"

It seems to me that our barrels are awfully good today, but if our aggs can be made smaller by indexing; I am all for it. Good shooting....James
 
If I remember correctly, big if there, there has been some work done on indexing center fire barrels by a few gunsmiths. The results seem to have been inconclusive. However that was I believe before tuners became popular. The more I think about it....indexing mght be why some barrels are hummers. They just happened to get indexed right when fitted. But who knows for sure. I am kind of with Gene. I don't think this is something that can be calculated. You just have to try it and see if it works. I still Like Vaughn's idea of how to fit a barrel to an action, but I don't how well that would work with a glue in action. Keep up the work Gene.
Donald
 
stiller said:
use a differential thread. Have an in between piece that threads into the action with different threads in the barrel. That way if you turn the barrel .25 turn in, move this same amount out and it gives the same headspace, just a different barrel index spot.
Click to expand...


Jerry! You 'da man! :D :D

Just had to say that one more time. :)

Hope everything is going well, my best regards to Curtis Helton and the rest of the gang at SPF. I'm looking forward to working with you guys on some new stuff in the future.

Later,

Gene Beggs
 
LOL.
I finally had to check in in this thread. I've seen the title...but until today never clicked on it. I have to laugh. It was what??? 9 months ago?, A year? Longer? Ago that Mr Calfee made some remark (or the remark was made in one of his threads) that you simply could not index a barrel in a threaded action. I pointed to the option of a differentially threaded bushing in that thread. Finally some indication that someone knew what I was talking about.
Thanks.
I've only read the last page of posts..I'll have to go back and catch up on the rest of what has got to be an interesting discussion. :D


Found it. :D
http://www.benchrest.com/forums/showpost.php?p=396529&postcount=23

Gene it was from your thread back in March.

And one from one of "Kathy"s threads in January.

http://www.benchrest.com/forums/showpost.php?p=378358&postcount=70
 
Last edited:
bglenn said:
Gene
How about putting a 2 to 1 ratio on your bushing? 16 thread action 32 thread for the barrel. Move bushing a 45 degree for every 90 degree you want to change the barrel. Bushing .0078 out (45º) and barrel .0078 in.(90º)

Glenn
Click to expand...

Glenn, I thought about that but I have something better in the works. I'll tell you about it as soon as I have the details worked out. The basic diffrential thread, bushing method works great and I am retaining that idea but I'm going about adjustments in a slightly different way.

Later

Gene Beggs
 
My set up is so much easier. I will be able to change the indexing of the barreled action in less than a minute. Loosen the pinch bolt, rotate the action to the new orientation, tighten the pinch bolt and shoot. PLUS, all that is required to adapt the bbl to the set up is provision for a 'recoil lug', aka a spacer between the bbl shoulder and the action.

In the pic below is a long piece of square tubing setting on two rests. Note the scope rings. This piece of square tubing would be fit in place of the forend in the second picture. The buttstock would be removed and a buttplate attached to the back of the receiver.

With this set up it will also be possible to verify the indexing after remachining the chamber and shoulder.

erectorsetbblindexingsetup.jpg

erectorsetcouplingcloseunscrewed.jpg

erectorsetthreadedsleeve.jpg
 
JD Mock said:
My question is, " How many of our top gunsmiths have experimented with indexing and what results did they get?" Good shooting....James
Click to expand...

Hi James,

I would say, "Darn few."

I can only speak for myself, but I'm convinced this is the biggest advancement in extreme rifle accuracy that has come along in many a day. :)

Every barrel that I have re-indexed after examining the barrel's signature on the target has shot much better than before. I have seen it time after time after time. I KNOW it works and I now have a much easier method of accomplishing that which at one time required two hours of machine work and a trip back to the shop. :D

Later,

Gene Beggs
 
You must log in or register to reply here.
Back
Top